useful

1. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 1/19
Multiple Pregnancy
Multiple pregnancy, or multifetal gestation, is a pregnancy with more than 1 fetus. Multiple pregnancy with more than 2
fetuses is referred to as a higher-order multiple pregnancy and the most common type of multiple pregnancy is a twin
pregnancy. Due to advanced maternal age and evolving assisted reproductive technology, the rates of multiple
pregnancies have steadily increased over the past 3 decades. However, rates have slowly plateaued with the increase of
the single embryo transfer. The perinatal mortality and morbidity rates of twin pregnancies are 3–7x higher than singleton
pregnancies primarily because of higher rates of preterm delivery. Multiple pregnancies also carry a higher risk of
obstetric complications such as congenital anomalies, preeclampsia, and gestational diabetes. Multiple pregnancies are
classified as high-risk and require astute obstetric care.
Last updated: December 3, 2021
CONTENTS
Overview
Classification and Diagnosis
Management

2. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 2/19
Overview
Definition
Multiple pregnancy is a pregnancy with more than 1 fetus.
Table: Important terminology of multiple pregnancy
Term Definition
Zygosity Refers to the genetic makeup of a twin pregnancy
Monozygotic twins Result from division of a single zygote
Share the same genetic material
Identical twins
Dizygotic twins Result from 2 separate eggs fertilized by 2 separate sperm
Share approximately 50% of the genetic material
Fraternal twins
Chorionicity The number of chorions (equal to the number of placentas)
Amnionicity The number of amnions surrounding the fetuses
Maternal Complications
Fetal Complications
References

3. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 3/19
Epidemiology
Statistics of the United States:
Twin births account for:
3% of live births
97% of multiple births
Dizygotic twins: 70% of all twin gestations in the absence of assisted reproductive technology
↑ Rate of monozygotic twins with assisted reproduction
Triplet and higher-order multiple births:
87.7 per 100,000 births
Approximately 80% are associated with medically assisted conception.
Risk factors
Prior history of multiple pregnancies
History of twins in the maternal family
Maternal weight and height: Women with a BMI ≥ 30 kg/m2 and ≥ 165 cm are at ↑ risk for dizygotic twin births.
↑ Maternal age
↑ Parity
Racial and ethnic variation:
↑ In Nigeria
↓ In Japan
Assisted reproductive technology or ovulation induction drugs
Classification and Diagnosis
Classification

4. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 4/19
Dizygotic twins are always dichorionic-diamniotic.
Monozygotic twins are classified based on the timing of cleavage after fertilization (timing of cleavage determines
chorionicity and amnionicity).
Table: Classification of monozygotic twins
Time of cleavage after fertilization Classification Prevalence
1–3 days Dichorionic-diamniotic 20%–25%
4–8 days Monochorionic-diamniotic 70%–75%
9–12 days Monochorionic-monoamniotic 1%–5%
≥ 13 days Monochorionic-monoamniotic (conjoined twins) Very rare

5. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 5/19

6. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 6/19

7. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 7/19
Diagnosis
Signs and symptoms:
Exaggerated early pregnancy symptoms (e.g., hyperemesis gravidarum)
Symphyseal-fundal height is greater than expected for gestational age.
↑ Abdominal girth
↑ Weight gain compared to singleton pregnancies

8. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 8/19
Ultrasound findings:
≥ 2 fetuses and ≥ 2 heart activities
Dichorionic-diamniotic:
Lambda sign: a thick, triangular protrusion of tissue leading up to the intertwin membrane
Thick intertwin membrane
2 separate placentas
Monochorionic-diamniotic:
T sign: the interface between 2 amniotic membranes
Thin intertwin membrane
Single placenta
Monochorionic-monoamniotic:
No intertwin membrane
Single placenta

9. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 9/19

10. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 10/19

11. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 11/19
Management
General care
Multiple pregnancy is considered a high-risk pregnancy.

12. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 12/19
Prenatal care requires:
More frequent prenatal visits
More frequent ultrasounds to monitor fetal growth
Adequate maternal nutrition
Monitoring for maternal complications (e.g., gestational diabetes and preeclampsia)
Monitoring for fetal complications (e.g., congenital anomalies)
Chorionicity determination is essential in the 1st trimester:
Aids in appropriate counseling of associated risks
Becomes less accurate after the beginning of the 2nd trimester
Mode of delivery
Depends on several factors, including:
Prior obstetric history
Current obstetric history
Fetal presentation of the twin closest to the birth canal (cephalic, or head presenting, is favorable for a vaginal
delivery)
The expertise of the obstetric provider
Multiple pregnancies with > 2 fetuses are almost always delivered by cesarean section.
Triplet pregnancies may be delivered vaginally by experienced obstetricians.
Timing of delivery in uncomplicated cases
For twins the timing for delivery depends on chorionicity and amnioniticy:
Dichorionic-diamniotic: 38 0/7 weeks–38 6/7 weeks
Monochorionic-diamniotic: 34 0/7 weeks–37 6/7 weeks
Monochorionic-monoamniotic: 32 0/7 weeks–34 0/7 weeks
Maternal Complications

13. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 13/19
Multiple pregnancy presents higher risk to develop complications such as:
Hyperemesis gravidarum
Gestational diabetes mellitus
Hypertensive pregnancy disorders (e.g., preeclampsia)
Anemia
Excessive weight gain
Postpartum hemorrhage (due to uterine atony or lacerations)
Miscarriages
Placental abnormalities (e.g., placenta previa)
Increased risk for cesarean delivery
Fetal Complications
Affecting all multiple pregnancies
Preterm labor and birth:
Resulting in prematurity and associated complications such as:
Respiratory failure
Intracranial hemorrhage
Sepsis
Cerebral palsy
Women with multifetal gestation are 6x more likely to give birth preterm.
Congenital anomalies
Low birth weight
Discordant growth
Neonatal death
Monochorionic twins
Twin-to-twin transfusion syndrome:

14. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 14/19
Occurs in 10%–15% of monochorionic twins
Due to arterio-venous anastomosis with imbalanced blood flow
Blood flows in a fixed direction from 1 fetus (donor) to another (recipient)
Donor twin:
Anemia
Growth restriction
Oligohydramnios
Recipient twin:
Polycythemia
Polyhydramnios
5 stages (each stage is progressively worse)
Management depends on the stage and severity of compromise and may include:
Monitoring
Amnioreduction
Fetoscopic laser occlusion of placental vessels
Selective feticide of 1 twin
Twin anemia polycythemia sequence (TAPS):
A form of atypical chronic twin-to-twin transfusion syndrome
Due to sparse vascular anastomoses
Characterized by:
Large difference in hemoglobin and reticulocyte levels between the twins
Absence of oligohydramnios and polyhydramnios
May occur either:
Spontaneously
Iatrogenically (after laser treatment for twin-to-twin transfusion syndrome)
Management: In the absence of poor prognostic factors, expectant management is appropriate.
Twin reversed arterial perfusion (TRAP):

15. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 15/19
Approximately 1% of monochorionic twins
Occurs when a twin with an absent/rudimentary heart is perfused by the other twin via abnormal placental anastomoses
(artery-to-artery shunt)
Donor twin:
Also called the “pump twin”
Suffers from high-output heart failure (e.g., polyhydramnios and cardiomegaly)
Recipient twin:
Also called the “acardiac twin”
Normally developed lower body, underdeveloped upper body
Management:
Focus on maximizing the outcome for the structurally normal pump twin.
Delivery is recommended for signs of cardiac compromise.

16. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 16/19

17. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 17/19

18. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 18/19
Monoamniotic twins
Umbilical cord entanglement
Conjoined twins:
Very rare: approximately 1 per 50,000–100,000 births
Requires expert care during pregnancy and after delivery
Separation after birth may be feasible but is associated with significant morbidity and mortality.
References

19. 8/2/23, 9:30 AM Multiple Pregnancy - Lecturio
https://app.lecturio.com/#/article/3761?return=__app__%2Fconcept%2Fcp%2F1234%2F4671%2F4846 19/19
1. Gabbe, S. G. (2017). Obstetrics: normal and problem pregnancies. (7th ed.). Elsevier.
2. Resnik, R., et al. (2019). Creasy and Resnik's maternal-fetal medicine: Principles and practice. Elsevier.
3. Cunningham, F. G. (2018). Williams obstetrics. New York: McGraw Hill Medical.
4. Chasen, S. (2021). Twin pregnancy: Overview. In Barss, V.A. (Ed.), UpToDate. Retrieved August 22, 2021, from
https://www.uptodate.com/contents/twin-pregnancy-overview
5. Mandy, G. T. (2020). Neonatal complications, outcome, and management of multiple births. In Kim, M.S. (Ed.), UpToDate. Retrieved August 24,
2021, from https://www.uptodate.com/contents/neonatal-complications-outcome-and-management-of-multiple-births
6. Hayes, E. J. (2021). Triplet pregnancy. In Barss, V.A. (Ed.), UpToDate. Retrieved September 15, 2021, from
https://www.uptodate.com/contents/triplet-pregnancy
7. Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies (2021). Obstetrics & Gynecology, 137(6). Retrieved September 15,
2021, from doi:10.1097/aog.0000000000004397
8. Moldenhauer, J. S. (2021). Multifetal pregnancy. MSD Manual Professional Version. Retrieved September 15, 2021, from
https://www.msdmanuals.com/professional/gynecology-and-obstetrics/abnormalities-and-complications-of-labor-and-delivery/multifetal-
pregnancy