1. Prenatal screening and diagnosis
- For prenatal screening
The screening tests, including non-invasive prenatal screening test (NIPT), first trimester combined nuchal translucency (NT) and biochemical screening (OSCAR) and mid-trimester biochemical screening can be used for twin pregnancies. To ensure adequate placental DNA from both twins in the maternal plasma, it is better to wait till 12 weeks or after before NIPT for twin pregnancies, compared with 10 weeks or after for singletons.
- For prenatal diagnosis
If it is a monochorionic (MC) twin pregnancy, both twins should be identical. Hence, sampling of one placenta (in the case of chorionic villous sampling) or one gestational sac (in the case of amniocentesis) is adequate.
If it is dichorionic (DC) twin pregnancy, the twins could be non-identical and therefore are of different chromosomal or genetic make-up. Therefore, both placentae or both gestational sacs need to be sampled for accurate diagnosis.
- Twins with one abnormality
Major anomaly affecting only one fetus occurs in approximately 1-2% of twin pregnancies. The choice is to have expectant management or selective feticide (i.e. to stop the fetal heart of the affected twin).
For DC twin pregnancies, it may be beneficial to have expectant management if the affected twin has a lethal anomaly (like trisomy 18 for instance). The procedure of selective feticide (see the section on ‘Multi-fetal reduction/ selective feticide’) carries a risk of miscarriage to the normal co-twin. However, if the abnormality is major but non-lethal, selective feticide might be a better option.
For MC twin pregnancies, expectant management is not appropriate if the fetal abnormality is associated with a risk of intrauterine fetal death. Fetal demise of the abnormal one can cause hypoxic-ischemic damage to the co-twin due to the vascular communication in the MC placentae. Therefore, selective feticide should be a better option. Selective feticide in MC pregnancy needs special consideration and will be discussed in the section on ‘Multi-fetal reduction/ selective feticide’.
2. Twin pregnancy with one intrauterine fetal demise
- If this happen in the first trimester, the surviving co-twin is usually not affected in both DC or MC twin pregnancies. On the other hand, if this happens in the second or the third trimester, the management depends on whether it is DC or MC twin pregnancies.
- For DC twin pregnancies, the placentae are separated and there is no worry of damage to the surviving co-twin due to vascular event as in the case of MC pregnancies. Hence, if the cause of the intrauterine fetal demise is unlikely to affect the surviving twin or the gestational age is still early, expectant management is appropriate. The neonatal outcome is good in general.
- For MC twin pregnancies, there is a significant risk to the co-twin. Please refer to ‘Specific risks of MC twins’ for further details.
3. Nutrition and supplementation
Nutrition for twin pregnancies is important but there is no need to ‘eat for 3’! Daily calorie intake of ~2,000 kcal is usually appropriate. Iron deficiency is more common among women with multiple pregnancies. Multi-vitamins supplementation containing iron, folic acid, DHA, calcium and vitamin D is advisable.
4. Assessment of fetal growth
Serial ultrasound assessment for fetal growth is needed for twin pregnancies. In case of significant discordant fetal growth, earlier delivery might be needed sometimes. It is a balance of the risks of fetal damage to the growth restricted twin if left in-utero and the risks of prematurity to the normally grown co-twin. For MC twins, closer ultrasound monitoring might be needed for twin-twin transfusion syndrome or other specific complications. (see ‘Specific risks of MC twins’)
5. Antenatal complications
- Prematurity
Preterm birth is main risk for twin pregnancies. The average gestational length is 36 weeks of gestation. Chorionicity also affects the risks of prematurity. The risk for preterm birth before 32 weeks is greater for MC twins (9.2%), compared with DC ones (5.5%).
- Other complications
Women with twin pregnancies were 3 times more likely to develop pre-eclampsia (gestational hypertension). They also have a higher chance of bleeding during pregnancy due to low-lying placenta (placental previa) and placental separation (placental abruptio). Gestational diabetes also appears to be more common in twin pregnancies.
Women with twin pregnancies may experience more significant pregnancy symptoms including nausea and vomiting in the first trimester, difficulty in movement due to the tummy size, easy tiredness, generalised oedema, difficulty with sleeping particularly in the late pregnancy.
6. Some tips for pregnant women with twins
- Early ultrasound at 6-8 weeks to determine whether it is DC or MC pregnancies
- Prenatal screening at 12 weeks with either OSCAR or NIPT; fetal morphology scan at 20 weeks
- Close serial ultrasound monitoring for twin-twin transfusion syndrome between 16-26 weeks for MC pregnancies
- Regular antenatal check-up, monitoring of blood pressure and ultrasound for fetal growth; look out for gestational diabetes
- Appropriate dietary intake and multi-vitamins supplementation – consult dietitian if needed
- Ensure adequate rest
- Rest legs more often or with stool – may help to minimize leg cramps
- Pillows or cushions for support during sleep
- Small but frequent meals to avoid full stomach and heart burn especially in the first and third trimesters
- Discuss with your obstetrician on the timing and mode of delivery
