Twin Pregnancy with Growth Discordance

Twin pregnancy with growth discordance is a twin pregnancy in which the estimated weights of the two fetuses differ by 20 percent or more. It results from unequal placental sharing, abnormal cord insertion, fetal anomaly, infection or chorionicity specific vascular problems. It matters because the smaller twin carries a high risk of death and a larger difference carries a worse outlook.

• Difference is calculated as (larger weight minus smaller weight) divided by larger weight, times 100.
• Risk factors: monochorionic placentation, velamentous or marginal cord insertion, maternal hypertension, smoking, previous growth restriction.
• A larger difference carries a higher perinatal mortality.

Women are often asymptomatic, with a uterus that measures differently from dates or a rapid change in size. Reduced fetal movements of one twin may be reported.

• Fundal height may be below dates.
• Hypertension in some.
• Differential diagnosis: twin to twin transfusion syndrome, selective growth restriction, twin anaemia polycythaemia sequence, wrong dates, normal growth variation, infection in one twin.
• Complications: death of the smaller twin, brain injury, preterm birth, preeclampsia, caesarean section, neonatal hypoglycaemia.

The approach is serial ultrasound with Doppler in both twins.

• Ultrasound every 2 to 4 weeks: estimated fetal weight for each twin, abdominal circumference, discordance percentage.
• Umbilical artery Doppler, middle cerebral artery Doppler and cerebroplacental ratio for both twins; deepest vertical pocket in each sac.
• Chorionicity from the first trimester scan; cord insertion sites; anomaly scan of each twin.
• Maternal blood pressure, urine protein, TORCH serology, malaria and syphilis tests; amniocentesis for karyotype if an anomaly is found.

The principle is surveillance by chorionicity and delivery before the smaller twin deteriorates.

• Supportive: scans every 1 to 2 weeks when discordance is 20 percent or more; daily fetal movement counts; admission for abnormal Doppler; birth in a unit with neonatal intensive care.
• Pharmacological: aspirin 150 mg oral at night from 12 weeks to 36 weeks; labetalol 200 mg oral every 8 to 12 hours (maximum 2.4 g daily) or nifedipine modified release 30 to 60 mg oral once daily (maximum 120 mg) for blood pressure 140/90 mmHg or more; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days when delivery is likely; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; ferrous sulphate 200 mg oral 8-hourly for anaemia; oxytocin 10 IU IM at birth.
• Procedures: delivery at 36 to 37 weeks for dichorionic twins with normal Doppler and at 34 to 36 weeks for monochorionic twins (earlier for abnormal Doppler); laser or cord occlusion in a fetal medicine unit for monochorionic complications; caesarean section for abnormal Doppler or tracing.
• Special groups: monochorionic twins with discordance need Doppler every week and referral for fetal medicine assessment for transfusion syndrome or selective growth restriction.
• Red flags: absent or reversed end diastolic flow in the small twin, reduced fetal movements, abnormal cardiotocography, polyhydramnios in the larger twin, preeclampsia.
• Follow-up: growth and Doppler scans every 1 to 2 weeks; cardiotocography twice weekly from 32 weeks; newborn glucose check at 2 hours, with glucose below 2.6 mmol/L treated by dextrose 10 percent 2 mL/kg IV over 10 minutes then 80 mL/kg per day.