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Screening and follow up of multiple pregnancy

Normal incidence of twins is 1 in 90 pregnancies (approximately 1/3 are monozygotic) and of triplets 1 in 8,100 pregnancies.

However, use of in vitro fertilisation (IVF) and ovulation induction techniques have greatly increased the incidence of multiple pregnancies to 1 in 60-74 pregnancies.

Women with multiple pregnancies should be offered a first trimester ultrasound scan when approximately 11 weeks 0 days to 13 weeks 6 days:[4]

Multiple pregnancies should be monitored carefully for intrauterine growth restriction (IUGR):

First-line management is usually laser surgery of inter-twin vascular placental anastomoses where the syndrome develops before 26 weeks of gestation.[6] Other options include intrauterine blood transfusions, serial amnioreduction or elective delivery.[7]

All twin pregnancies (regardless of chorionicity) are regularly scanned after about 30 weeks to monitor growth and fetal well-being, with early delivery induced in cases of growth cessation and/or poor Doppler blood flow indices.

The women should be informed about the greater likelihood of Down’s syndrome in twin and triplet pregnancies before screening. They should be made aware of the different options for screening and the higher false-positive rate of screening tests in twin and triplet pregnancies. As a result of this they have a greater likelihood of being offered invasive testing and of complications occurring from this testing. Screening should be performed between approximately 11 weeks 0 days and 13 weeks 6 days:

If one fetus is detected as abnormal, selective termination (if desired) can be performed .