Newborn Care: Assessing gestational age and size at birth


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Newborn Care was written for healthcare workers providing special care for newborn infants in level 2 hospitals. It covers: resuscitation at birth, assessing infant size and gestational age, routine care and feeding of both normal and high-risk infants, the prevention, diagnosis and management of hypothermia, hypoglycaemia, jaundice, respiratory distress, infection, trauma, bleeding and congenital abnormalities, communication with parents

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Newborn Care: Assessing gestational age and size at birth

  1. 1. 2 Assessing gestational age and size at birth ASSESSING AN INFANT’SObjectives GESTATIONAL AGE ATWhen you have completed this unit you BIRTHshould be able to:• Define the normal range of gestational 2-1 What is gestational age? age. Gestational age (or the duration of pregnancy)• List the complications of preterm and is measured in weeks from the first day of the postterm infants. mother’s last normal menstrual period to the• Define the normal range of weight at day of delivery. birth. NOTE ‘Gestational age’ or menstrual age differs• Divide infants into groups by gestational from post-conceptual age, which is the duration from conception to birth. Post-conceptual age is age and weight. 2 weeks less than gestational age. It is important• List the causes and complications to remember this when assessing the gestational of underweight and overweight for age of infants conceived by in vitro fertilisation. gestational age infants.• Recognise the signs of wasting. 2-2 What is the average gestational age?• List the complications of wasted infants. The average gestational age is 40 weeks (280 days). Not all women with normal pregnancies deliver at exactly 40 weeks however. A range of 37 weeks (259 days) to 42 weeks (294 days) is accepted as normal. Infants with a normal gestational age are called term infants. Most infants are born at
  2. 2. 44 NEWBORN CAREterm and these infants have the lowest risk of 3. A clinical scoring test can be used to assessproblems in the newborn period. more accurately the infant’s gestational age. The Ballard method of scoring an infant’s gestational age is based on both the infant’s Most infants are born between 37 and 42 weeks physical appearance and behaviour. of gestation NOTE Other scoring systems such as the Finnstrom and the Dubowitz methods can also2-3 When is the duration of pregnancy too be used to assess the gestational age of infants.short or too long? A modification of the original Ballard method is now used to give a more accurate assessment1. Infants that are born before 37 weeks are of gestational age in infants less than 32 weeks. called preterm infants. About 5% of all Wasted and growth-restricted infants tend to infants are born preterm in an affluent underscore. community and often more than 20% in a poor community. Preterm infants have a 2-5 What are the common complications of high risk of neonatal problems. Therefore, a preterm infant? any pregnancy ending before 37 weeks is regarded as too short. These infants have immature organs because2. Infants with a gestational age of 42 weeks they are born too soon. They are also small or more are called postterm infants. and fragile and can, therefore, be easily About 5% of infants are born postterm. damaged at delivery. As these infants also have an increased The common neonatal complications in risk of neonatal problems, a pregnancy of infants born preterm are: 42 weeks or more is regarded as too long. 1. Neonatal asphyxia 2. Hypothermia Infants born before 37 weeks gestation are called 3. Hypoglycaemia preterm infants 4. Hyaline membrane disease 5. Recurrent apnoea NOTE The words ‘premature’ and ‘postmature’ are 6. Poor feeding no longer used as they are confusing and difficult 7. Jaundice to define. 8. Infection 9. Anaemia2-4 How do you assess the gestational age 10. Intraventricular haemorrhageof an infant? 11. Patent ductus arteriosus 12. Separation from parents1. If possible the gestational age should be determined before delivery from the Preterm infants are therefore at high risk mother’s menstrual history and clinical of many complications after birth and need examination in early pregnancy. An special care. Many preterm infants die as a ultrasound examination before 20 weeks result of these complications. is also an accurate method of determining the gestational age. Preterm infants have an increased risk of2. If the duration of pregnancy is unknown or uncertain, the gestational age can be problems due to organ immaturity roughly estimated by simply observing the infant’s appearance and behaviour. This is 2-6 What are the common complications of an inaccurate method, however, unless the a postterm infant? examiner is very experienced. 1. These infants usually are large, due to the prolonged period of intra-uterine growth
  3. 3. ASSESSING GESTATIONAL AGE AND SIZE AT BIR TH 45 and, therefore, may experience birth All infants must be weighed at birth because trauma due to cephalopelvic disproportion, birth weight can be used to divide infants into e.g. fractured clavicle or Erb’s palsy.2. Commonly the placenta is unable to high-risk and low-risk categories provide the large fetus with enough energy and oxygen during the last extra weeks of 2-9 How do you group infants by their birth pregnancy. Therefore, there is an increased weight? risk of fetal distress during labour and also soft tissue wasting with hypoglycaemia Infants can be divided into groups by their soon after birth. birth weight. This is particularly useful if the gestational age is not known. Most infants Postterm infants often suffer trauma, hypoxia weigh between 2500 g and 4000 g at birth. and hypoglycaemia These infants are usually healthy and require only routine care. Infants weighing less than 2500 g and infants weighing 4000 g or more have an abnormal birth weight and are at anASSESSING AN INFANT’S increased risk of neonatal problems. They therefore may require special care.SIZE AT BIRTH Infants weighing less than 2500 g are called low birth weight (LBW) infants.2-7 How do you determine an infant’s sizeafter delivery? Low birth weight infants weigh less than 2500 g,The size of a newborn infant is usually often have clinical problems in the newborndetermined by weighing the naked infant period and may need extra careafter birth. While weight is often the onlymeasurement of size that is determined afterbirth, it is also useful to measure the infant’shead circumference. Sometimes the crown- GROUPING INFANTSheel length is also measured at birth. However, BY THEIR WEIGHT FORlength is difficult to measure accurately and,therefore, is usually not recorded routinely. GESTATIONAL AGE2-8 Why should you determine an infant’s 2-10 How can you group infants by theirbirth weight? weight for gestational age?After delivery all infants should be weighed Weight for gestational age can also be used tobecause: group newborn infants into low-risk and high-1. Weight is commonly used to determine an risk categories. infant’s size at birth as it is both easy and It is, therefore, possible to group infants into accurate to measure. low-risk and high-risk categories by their:2. Infants with an abnormally low or abnormally high birth weight have an 1. Gestational age alone. increased risk of neonatal problems. 2. Weight alone. Measuring birth weight is a simple method 3. Weight for gestational age (weight and of identifying these high-risk infants. gestational age together).3. Birth weight is important in assessing Each method is useful as it tells you something subsequent weight gain or loss during the different about an infant. first week of life.
  4. 4. 46 NEWBORN CARE2-11 How do you determine weight for 2. Infants with a birth weight for theirgestational age? gestational age that falls above the 90th centile are called overweight for gestationalOnce you have weighed an infant and assessed age infants. These infants have grown fasterthe gestational age, this information can be than normal during pregnancy and weighplotted on a weight for gestational age chart. more than expected.Gestational age is plotted in weeks along 3. Infants with a birth weight for theirthe bottom of the chart and is divided into gestational age that falls below thepreterm, term and postterm categories. Birth 10th centile are called underweight forweight in grams is plotted on the left hand gestational age infants. These infantsmargin of the chart. Note that the birth weight have grown slower than normal duringsteadily increases with gestational age: pregnancy and weigh less than expected.1. On the chart are 2 lines called the 10th and 90th centiles. Infants with a normal birth weight for their gestational age fall between Underweight for gestational age infants weigh the 10th and 90th centiles. As their weight less than expected and have a birth weight which is appropriate for their gestational age they falls below the 10th centile are referred to as appropriate for gestational age infants (AGA infants). These infants In a well-nourished community 80% of have grown normally during pregnancy. infants will be appropriate for gestationalBirth weight (g)50004000300020001000 500 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 Gestational age (weeks)Figure 2.1: Weight for gestational age chart.
  5. 5. ASSESSING GESTATIONAL AGE AND SIZE AT BIR TH 47age, 10% overweight and 10% underweight for gestational age commonly have problemsfor gestational age. However, in a poor during the first weeks of life. It is important,community there may be far more therefore, to identify these infants as soon asunderweight and far fewer overweight for possible after delivery. Infants that are born atgestational age infants. term and are appropriate for their gestational NOTE The descriptions ‘small-for-gestational- age have the lowest risk of problems in the age’ (SGA) and ‘large-for-gestational-age’ (LGA) newborn period and, therefore, usually need are also used. However, overweight (OGA) and routine care only. underweight for gestational age (UGA) are preferable as they specify that weight is being assessed. Many UGA infants have a normal length Underweight and overweight for gestational age and head circumference. Therefore, they are not infants commonly have complications during the really small but rather thin or wasted. first weeks of life Many weight for gestational age standards (charts) have been used. They differ depending An infant’s head circumference can also be on the nutritional status of the study population. plotted against gestational age on a head The international weight for gestational age circumference for gestational age chart. standard used in this unit is both simple and The method is the same as that used for useful to screen infants. Head circumference and plotting weight for gestational age. Head length standards may also be used to further classify infants. circumferences between the 10th and 90th centiles are regarded as normal for gestational age. A head circumference above the 90th2-12 Why do some infants weigh more than centile is abnormally large while a headothers? circumference below the 10th centile isYou will now understand that a heavy infant abnormally small for gestational age. A headmay weigh more than usual at delivery circumference below the 10th centile indicatesbecause the infant is either: that the infant’s brain is small and has not grown at the normal rate.1. Postterm.2. Overweight for gestational age.3. Both postterm and overweight for 2-14 What are the causes of an infant being gestational age. born overweight for gestational age?Likewise a low birth weight infant may weigh There are 2 main causes of a fetus growingless than usual at delivery because the infant is faster than usual, resulting in an overweighteither: for gestational age infant:1. Preterm 1. A heavy or obese mother.2. Underweight for gestational age, or 2. A diabetic mother.3. Both preterm and underweight for However, in many cases the cause of the infant gestational age. being overweight for gestational age is not known. Low birth weight infants are not all born preterm Infants born to diabetic women are often2-13 What is the value of plotting an overweight for gestational ageinfant’s weight for gestational age?The exercise of classifying all newborn infantsby their weight for gestational age is extremelyuseful as infants born overweight forgestational age and infants born underweight
  6. 6. 48 NEWBORN CARE2-15 What are the complications of 2-17 What is the clinical appearance of anoverweight for gestational age infants? underweight for gestational age infant?Overweight for gestational age infants are at This will depend on whether the cause ofan increased risk of neonatal problems: slow fetal growth affected the fetus from early pregnancy or only during the last few weeks of1. They are usually large and obese and, pregnancy: therefore, may experience birth trauma due to cephalopelvic disproportion. 1. If intra-uterine growth restriction (IUGR)2. Infants that are overweight for gestational was present for many months, the age because their mothers are poorly infant will appear symmetrically small controlled diabetics are at high risk of at delivery with a birth weight and head hypoglycaemia and respiratory distress circumference (and length) below the 10th after delivery. They also commonly have centile. These infants have been growing congenital abnormalities. slowly for a long time. 2. If the fetal growth was only affected during2-16 What are the causes of an infant being the last weeks of pregnancy, then the infantborn underweight for gestational age? will be wasted at delivery. These infantsThere are both maternal and fetal causes of appear to have recently lost weight and,slow fetal growth resulting in the birth of an therefore, look starved. They have sufferedunderweight for gestational age infant. acute undernutrition for a few weeks. Therefore only the weight will be below the1. Maternal causes: 10th centile. The head circumference (and • Low maternal weight length) will be above the 10th centile. • Smoking 3. Some infants will have the features of • Excess alcohol intake both intra-uterine growth restriction and • Hypertension wasting. These infants have grown slowly2. Fetal causes: for months during pregnancy followed by • Multiple pregnancy weight loss during the last weeks before • Chromosomal abnormalities, e.g. delivery. Although their weight and head Down syndrome circumference will both be below the • Severe congenital abnormalities 10th centile, weight will fall below head • Chronic intra-uterine infections, e.g. circumference on the chart. syphilis NOTE Some underweight for gestational ageMaternal hypertension and smoking result in infants are not wasted but have simply growndecreased blood flow to the placenta. However, slowly since early pregnancy. These infantsin many cases no obvious cause can be found. usually have underweight mothers and grow slowly in order to protect themselves from starvation, which might occur towards term Pregnant women should not smoke or drink if they grew faster and had greater nutritional alcohol needs. In this case IUGR may be an appropriate response to a poor environment. These infants NOTE Placental causes are rare. Chronic continue to grow slowly after birth. hypertension, pre-eclampsia (gestational proteinuric hypertension) and smoking are 2-18 What are the clinical signs of wasting maternal causes as the problem is in the spiral arteries not the placenta. in a newborn infant? Wasting of the soft tissues, such as muscle and subcutaneous fat, may be recognised in the infant at birth by the following features:
  7. 7. ASSESSING GESTATIONAL AGE AND SIZE AT BIR TH 491. Dry, peeling skin birth. Therefore, all wasted infants, even if2. Loose, wrinkled skin and little muscle, they are born at term and have a birth weight especially in the upper legs, giving the between the 10th and 90th centiles, are at an appearance that the infant has recently lost increased risk of those problems expected weight in underweight for gestational age infants, i.e. neonatal asphyxia, hypoxia, meconiumThese clinical signs suggest that the fetus has aspiration, hypothermia and hypoglycaemia.been undernourished during the last weeksof pregnancy and, as a result, has very few NOTE When a wasted infant with a birth weightenergy stores at birth (i.e. little glycogen, fat that is appropriate for gestational age is plottedand muscle). on the chart, the infant’s weight will be lower than the head circumference, although both measurements still fall between the 10th and2-19 What are the common complications 90th centiles.of an underweight for gestational ageinfant? All wasted infants are at an increased risk ofAll underweight for gestational age infants, problems in the newborn period, even if they arewhether they are wasted or not, are at an not underweight for gestational ageincreased risk during the first weeks of lifebecause they have often received too little foodand oxygen during pregnancy. Underweight 2-21 Which infants need their gestationalfor gestational age infants, therefore, need age and weight assessed at birth?special care after delivery. The gestational age should be clinicallyThe common complications of infants born assessed and the weight measured in all infantsunderweight for gestational age are: at delivery. Many women will know their duration of pregnancy. With experience the1. Neonatal asphyxia gestational age can be roughly estimated by2. Organ damage due to lack of oxygen before simple observation alone. As the Ballard score delivery (hypoxia) takes time to perform, it is not done routinely3. Meconium aspiration on all infants. However, the following high-4. Hypothermia risk infants should be scored by the Ballard5. Hypoglycaemia method if the gestational age is uncertain. InIf the infant is born underweight for addition their weight should be accuratelygestational age because of congenital measured and plotted on the weight forabnormalities, chromosomal abnormalities gestational age chart:(e.g. Down syndrome) or chronic intra-uterine 1. Infants who are preterm or postterm byinfections (e.g. syphilis), then these causes will dates or appearancealso result in clinical problems. 2. Infants with a birth weight below 2500 g or above 4000 g2-20 Are all wasted infants either postterm 3. Wasted infantsor underweight for gestational age? 4. Clinically ill infantsNo. Although many wasted infants are The risk of complications can be best assessedpostterm or underweight for gestational age, if both birth weight and gestational agesome wasted infants are born at term with are known and weight for gestational agea birth weight that is appropriate for their determined.gestational age. These infants have only beenstarved for a few days before delivery and,therefore, have not lost enough weight to Gestational age should be accurately determinedbecome underweight for gestational age at in all high-risk infants
  8. 8. 50 NEWBORN CARE2-22 Why are all infants not the same size 2-23 What is the value of measuring theat birth? head circumference at birth?You should realise by now that all newborn An accurate measurement of the headinfants are not the same size at birth because circumference at birth is very helpful andthe gestational age and weight may vary should be done routinely. A normal headwidely and they may or may not be wasted. circumference (and length) for gestationalSimilarly all infants do not have the same risk age at birth indicates that the infant hasof neonatal problems. By dividing infants into grown normally during pregnancy. A normalseparate groups, using gestational age, weight head circumference but low weight forand wasting, you should be able to identify gestational age suggests wasting. Knowinghigh-risk infants and also predict the sort of the head circumference at birth assists in theproblems that a particular infant will develop clinical assessment of an older child withduring the first weeks of life. This is extremely developmental delay or cerebral palsy.important as many of these problems arepreventable with correct management soon 2-24 Do low birth weight infants growafter delivery. normally after birth?At the birth of every infant, the following 3 It depends on the reason for being low birthquestions should be asked: weight. Preterm, wasted or underweight for1. What is the gestational age? gestational age infants with a normal head2. What is the birth weight? circumference and length for gestational age3. Does the infant have dry, peeling skin and at birth usually grow well during childhood. appear starved? However, infants with a head circumference and length below the 10th centile at birthIf any of these 3 questions reveals an abnormal usually remain small for their age as childrenresult, then you should ask whether the infant’s and become short adults.weight for the gestational age falls within thenormal range (i.e. between the 10th and 90thcentiles)? With all this information you will be CASE STUDY 1able to answer the following questions:1. Is the duration of pregnancy too short or A woman presents in labour at a level 1 clinic. too long? By her dates and abdominal palpation she is2. Does the infant have a low birth weight? 32 weeks pregnant. After a short labour she3. Is the infant overweight or underweight for delivers a male infant weighing 1400 g. The gestational age? Ballard score confirms the gestational age. The4. Is the infant wasted? infant’s weight falls between the 10th and 90thNow you should be able to decide whether the centiles.infant is at high risk or low risk of problemsand what level of care is needed during the 1. How would you classify this infant byfirst days of life. weight alone? This is a low birth weight infant as the weight A risk assessment should be done on all infants is less than 2500 g. at birth 2. How would you classify this infant by gestational age alone? The infant is preterm because the infant was born before 37 weeks of gestation.
  9. 9. ASSESSING GESTATIONAL AGE AND SIZE AT BIR TH 513. How would you classify this infant by 4. How would you classify this infant byweight for gestational age? weight for gestational age?The infant should be classified as appropriate This infant is underweight for gestational age.for gestational age because the weight fallswithin the normal range for gestational age. 5. Why is it important to identify this infant as being both underweight for gestational4. What problems is this infant at high risk age and wasted?of in the first few weeks of life? Because the diagnosis places the infant at highAs a preterm, appropriate for gestational risk of neonatal asphyxia, meconium aspiration,age infant, the important risks after delivery hypothermia and hypoglycaemia. The infantare neonatal asphyxia, hypothermia, may also have organ damage due to the lack ofhypoglycaemia, hyaline membrane disease, oxygen before delivery (prenatal hypoxia).apnoea, poor feeding, jaundice, infection,anaemia, intraventricular haemorrhage, 6. Are all postterm infants wasted orpatent ductus arteriosus and separation from underweight for gestational age?the parents. Management must, therefore, beaimed at preventing or treating these problems. No, but postterm infants often are wasted or underweight for gestational age.CASE STUDY 2 7. What is the probable cause of this infant being underweight for gestational age?A female infant weighs 2200 g at birth. The The mother’s heavy smoking.mother is unbooked and does not know thedate of her last menstrual period. She smokes20 cigarettes a day. The infant has loose, CASE STUDY 3wrinkled, dry skin. The infant scores at 42.5weeks on the Ballard score. When plotted on a A woman who booked early and attended anweight for gestational age chart, the infant falls antenatal clinic regularly delivers an infant at abelow the 10th centile. level 1 clinic. She is 39 weeks by dates and the infant appears to be of normal size. The infant1. What is the explanation for the appears normal and feeds well. The birthappearance of this infant’s skin? weight is 3100 g.The loose, wrinkled, dry skin suggests softtissue wasting due to an inadequate supply 1. Why should this infant be weighed?of food to the fetus during the last weeks of All infants should be weighed routinely afterpregnancy. delivery, even if they appear normal and healthy, in order to identify low birth weight2. Why was it important to score this infant? infants. An accurate birth weight is alsoBecause the patient did not know the duration important to determine weight gain or lossof pregnancy and because the infant weighed during the first days and weeks after birth.less than 2500 g and was wasted. 2. Should you score this infant’s gestational3. How would you classify this infant by age?gestational age alone? There is no need to score this infant as theThe scored age of 42.5 weeks indicates that the mother knows her menstrual dates and theinfant was born postterm. infant appears normal.
  10. 10. 52 NEWBORN CARE3. How would you classify this infant by its 3. Why should this infant receive more thanweight and gestational age? just primary care?This is a term, appropriate-for-gestational- Because infants of diabetic women, especiallyage infant and, therefore, is at low risk for if they are preterm and overweight forproblems in the newborn period. As the infant gestational age, are at high risk of problems inalso appears normal and feeds well, the infant the first weeks of life.should receive routine, primary care at thelevel 1 clinic. CASE STUDY 54. Are all infants who weigh 3100 g born atterm? A woman who has hypertension andMost will be term infants. However, some may proteinuria (i.e. pre-eclampsia) for the lastbe underweight for gestational age postterm month of pregnancy delivers at 38 weeks. Theinfants while others may be overweight for infant appears wasted but has a birth weightgestational age preterm infants. between the 10th and 90th centiles. The Apgar scores were low and the infant required resuscitation.5. Should you measure this infant’s headcircumference and length? 1. How would you classify this infant?Head circumference should be measuredroutinely after birth. However, length is Term and appropriate for gestational age.difficult to measure accurately and usually isnot recorded. 2. Why is this infant at high risk of problems during the first weeks of life? Because the infant is wasted. Even though thisCASE STUDY 4 infant is appropriate for gestational age and born at term, the risk of clinical problems isAn obese diabetic patient delivers an infant high because of the 36.5 weeks. The infant appears very fat andweighs 3700 g. 3. What is the probable cause of the wasting?1. How would you classify this infant? The maternal pre-eclampsia. As a result ofPreterm and overweight for gestational age decreased placental blood flow, the fetus didas the infant was born before 37 weeks and not receive enough energy (calories) duringmust be above the 90th centile with a weight of the last few weeks of pregnancy and, therefore,3700 g. This should be confirmed by plotting became wasted due to weight loss.the infant’s weight for gestational age on achart. 4. What was the probable cause of the neonatal asphyxia?2. What is the probable cause of the infant Hypoxia during labour. Wasted infants are atbeing overweight for gestational age? high risk of fetal hypoxia.The mother’s diabetes and obesity.