Each year approximately 4000 twins, 100 triplets and quadruplets are born. Epidemiological data shows that multiple births are on the rise, with a 35% increase in twins, and a 300% increase in triplets and quadruplets. Most triplets (60%) and quadruplets (90%) are the result of infertility treatment, mostly due to the various ovulation inductions.
Overall, the incidence of twins is 1 in 80 births. Of these, 1 in 250 are stable monozygotic twins, and the rest are dizygotic, though that figure is significantly increasing as a result of fertility therapy.
Multiple gestations are investigated if there are clinical risk factors or if the pregnant woman is large for her dates. Ultrasound is used for ultimate diagnosis.
Ultrasound is also used to determine chorionicity, which may have implications in the management of the pregnancy. An attempt is made to determine the fetal sex (if different, then it must be dichorionic), the number of placenta, twin peak signs, membrane thickness, or layers.
Monochorionic twin pregnancies have an increased risk fetal anomalies, increased perinatal mortality, and some incidence of placental vascular communications, namely twin-twin transfusion syndrome.
In the mother, potential complications include hyperemisis, anemia, gestational diabetes, preeclampsia, cesarian section, placental abruption, or postpartum hemorrhage. In the newborn, complications include congenital abnormalities, premature birth, a fetal growth restriction, and twin-twin syndrome.
As such, management must foremost include heightened maternal/fetal surveillance, as well as some lifestyle alterations, serial ultrasounds to assess growth, and a thorough recheck of fetal wellbeing after 34 weeks.