1 Guidance

The following guidance is based on the best available evidence. The full guideline gives details of the methods and the evidence used to develop the guidance.

This guideline should be read in conjunction with 'Antenatal care' NICE clinical guideline 62. This guideline specifies the care that women with twin and triplet pregnancies should receive that is additional or different from routine antenatal care for women with singleton pregnancies. Table 5.8 in the full guideline shows a comparison of the schedule of appointments for women with singleton pregnancies and women with multiple pregnancies.

Note that for many women the twin or triplet pregnancy will be detected only after their routine booking appointment. Women should then be offered the specialist antenatal appointments as outlined in section 1.2.3.

1.1 Determining gestational age and chorionicity

See appendix E for definitions of key terms used in this guideline (including chorionicity and amnionicity).

1.1.1 Gestational age

1.1.1.1 Offer women with twin and triplet pregnancies a first trimester ultrasound scan when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days) to estimate gestational age, determine chorionicity and screen for Down's syndrome (ideally, these should all be performed at the same scan; see 1.1.2.1 and 1.1.2.2)[3].

1.1.1.2 Use the largest baby to estimate gestational age in twin and triplet pregnancies to avoid the risk of estimating it from a baby with early growth pathology.

1.1.2 Chorionicity

1.1.2.1 Determine chorionicity at the time of detecting twin and triplet pregnancies by ultrasound using the number of placental masses, the lambda or T-sign and membrane thickness.

1.1.2.2 Assign nomenclature to babies (for example, upper and lower, or left and right) in twin and triplet pregnancies and document this clearly in the woman's notes to ensure consistency throughout pregnancy.

1.1.2.3 If a woman with a twin or triplet pregnancy presents after 14 weeks 0 days, determine chorionicity at the earliest opportunity by ultrasound using all of the following:

  • the number of placental masses

  • the lambda or T-sign

  • membrane thickness

  • discordant fetal sex.

1.1.2.4 If it is not possible to determine chorionicity by ultrasound at the time of detecting the twin or triplet pregnancy, seek a second opinion from a senior ultrasonographer or offer the woman referral to a healthcare professional who is competent in determining chorionicity by ultrasound scan as soon as possible.

1.1.2.5 If it is difficult to determine chorionicity, even after referral (for example, because the woman has booked late in pregnancy), manage the pregnancy as monochorionic until proved otherwise.

1.1.2.6 Provide regular training so that ultrasonographers can identify the lambda or T-sign accurately and confidently. Less experienced ultrasonographers should have support from senior colleagues.

1.1.2.7 Training should cover ultrasound scan measurements needed for women who book after 14 weeks 0 days and should emphasise that the risks associated with twin and triplet pregnancies are determined by chorionicity and not zygosity.

1.1.2.8 Conduct regular clinical audits to evaluate the accuracy of determining chorionicity.

1.1.2.9 If transabdominal ultrasound scan views are poor because of a retroverted uterus or a high body mass index (BMI), use a transvaginal ultrasound scan to determine chorionicity.

1.1.2.10 Do not use three-dimensional ultrasound scans to determine chorionicity.

1.1.2.11 Networks should agree care pathways for managing all twin and triplet pregnancies to ensure that each woman has a care plan in place that is appropriate for the chorionicity of her pregnancy.

1.2 General care

1.2.1 Information and emotional support

1.2.1.1 Explain sensitively the aims and possible outcomes of all screening and diagnostic tests to women with twin and triplet pregnancies to minimise their anxiety.

1.2.2 Diet, lifestyle and nutritional supplements

1.2.2.1 Give women with twin and triplet pregnancies the same advice about diet, lifestyle and nutritional supplements as in routine antenatal care[4].

1.2.2.2 Be aware of the higher incidence of anaemia in women with twin and triplet pregnancies compared with women with singleton pregnancies.

1.2.2.3 Perform a full blood count at 20–24 weeks to identify women with twin and triplet pregnancies who need early supplementation with iron or folic acid, and repeat at 28 weeks as in routine antenatal care[5].

1.2.3 Specialist care

1.2.3.1 Clinical care for women with twin and triplet pregnancies should be provided by a nominated multidisciplinary team consisting of:

  • a core team of named specialist obstetricians, specialist midwives and ultrasonographers, all of whom have experience and knowledge of managing twin and triplet pregnancies

  • an enhanced team for referrals, which should include:

    • a perinatal mental health professional

    • a women's health physiotherapist

    • an infant feeding specialist

    • a dietitian.

      Members of the enhanced team should have experience and knowledge relevant to twin and triplet pregnancies.

1.2.3.2 Referrals to the enhanced team should not be made routinely for women with twin and triplet pregnancies but should be based on each woman's needs.

1.2.3.3 Coordinate clinical care for women with twin and triplet pregnancies to:

  • minimise the number of hospital visits

  • provide care as close to the woman's home as possible

  • provide continuity of care within and between hospitals and the community.

1.2.3.4 The core team should offer information and emotional support specific to twin and triplet pregnancies at their first contact with the woman and provide ongoing opportunities for further discussion and advice including:

  • antenatal and postnatal mental health and wellbeing

  • antenatal nutrition (see 1.2.2.1)

  • the risks, symptoms and signs of preterm labour and the potential need for corticosteroids for fetal lung maturation

  • likely timing and possible modes of delivery[6]

  • breastfeeding

  • parenting.

1.2.3.5 Offer women with uncomplicated monochorionic diamniotic twin pregnancies at least nine antenatal appointments with a healthcare professional from the core team. At least two of these appointments should be with the specialist obstetrician.

  • Combine appointments with scans when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days) and then at estimated gestations of 16, 18, 20, 22, 24, 28, 32 and 34 weeks (see 1.7.1.1)[7].

1.2.3.6 Offer women with uncomplicated dichorionic twin pregnancies at least eight antenatal appointments with a healthcare professional from the core team. At least two of these appointments should be with the specialist obstetrician.

  • Combine appointments with scans when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days) and then at estimated gestations of 20, 24, 28, 32 and 36 weeks (see 1.7.1.1)[7].

  • Offer additional appointments without scans at 16 and 34 weeks.

1.2.3.7 Offer women with uncomplicated monochorionic triamniotic and dichorionic triamniotic triplet pregnancies at least 11 antenatal appointments with a healthcare professional from the core team. At least two of these appointments should be with the specialist obstetrician.

  • Combine appointments with scans when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days) and then at estimated gestations of 16, 18, 20, 22, 24, 26, 28, 30, 32 and 34 weeks (see 1.7.1.1)[7].

1.2.3.8 Offer women with uncomplicated trichorionic triamniotic triplet pregnancies at least seven antenatal appointments with a healthcare professional from the core team. At least two of these appointments should be with the specialist obstetrician.

  • Combine appointments with scans when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days) and then at estimated gestations of 20, 24, 28, 32 and 34 weeks (see 1.7.1.1)[7].

  • Offer an additional appointment without a scan at 16 weeks.

1.2.3.9 Women with twin and triplet pregnancies involving a shared amnion should be offered individualised care from a consultant in a tertiary level fetal medicine centre (see 1.6.1.1).

1.3 Fetal complications

1.3.1 Information about screening

1.3.1.1 A healthcare professional with experience of caring for women with twin and triplet pregnancies should offer information and counselling to women before and after every screening test.

1.3.1.2 Inform women with twin and triplet pregnancies about the complexity of decisions they may need to make depending on the outcomes of screening, including different options according to the chorionicity of the pregnancy.

1.3.2 Screening for Down's syndrome

1.3.2.1 Before screening for Down's syndrome offer women with twin and triplet pregnancies information about:

  • the greater likelihood of Down's syndrome in twin and triplet pregnancies

  • the different options for screening[4]

  • the false positive rate of screening tests, which is higher in twin and triplet pregnancies

  • the likelihood of being offered invasive testing, which is higher in twin and triplet pregnancies

  • the greater likelihood of complications of invasive testing

  • the physical risks and psychological implications in the short and long term relating to selective fetal reduction.

1.3.2.2 Healthcare professionals who screen for Down's syndrome in twin pregnancies should:

  • map the fetal positions

  • use the combined screening test (nuchal translucency, beta-human chorionic gonadotrophin, pregnancy-associated plasma protein-A) for Down's syndrome when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days; see 1.1.1.1)

  • calculate the risk of Down's syndrome per pregnancy in monochorionic twin pregnancies

  • calculate the risk of Down's syndrome for each baby in dichorionic twin pregnancies.

1.3.2.3 Healthcare professionals who screen for Down's syndrome in triplet pregnancies should:

  • map the fetal positions

  • use nuchal translucency and maternal age to screen for Down's syndrome when crown–rump length measures from 45 mm to 84 mm (at approximately 11 weeks 0 days to 13 weeks 6 days; see 1.1.1.1)

  • calculate the risk of Down's syndrome per pregnancy in monochorionic triplet pregnancies

  • calculate the risk of Down's syndrome for each baby in dichorionic and trichorionic triplet pregnancies.

1.3.2.4 Where first trimester screening for Down's syndrome cannot be offered to a woman with a twin pregnancy (for example, if the woman books too late in pregnancy) consider second trimester serum screening and explain to the woman the potential problems of such screening. These include the increased likelihood of pregnancy loss associated with double invasive testing because the risk of Down's syndrome cannot be calculated separately for each baby.

1.3.2.5 Do not use second trimester serum screening for Down's syndrome in triplet pregnancies.

1.3.2.6 Offer women with twin and triplet pregnancies who have a high risk of Down's syndrome (use a threshold of 1:150 as defined by the NHS Fetal Anomaly Screening Programme [FASP][8]) referral to a fetal medicine specialist in a tertiary level fetal medicine centre.

1.3.3 Screening for structural abnormalities

1.3.3.1 Offer screening for structural abnormalities (such as cardiac abnormalities) in twin and triplet pregnancies as in routine antenatal care[9].

1.3.3.2 Consider scheduling ultrasound scans in twin and triplet pregnancies at a slightly later gestational age than in singleton pregnancies and be aware that the scans will take longer to perform.

1.3.3.3 Allow 45 minutes for the anomaly scan in twin and triplet pregnancies (as recommended by FASP)[8].

1.3.3.4 Allow 30 minutes for growth scans in twin and triplet pregnancies.

1.3.4 Monitoring for feto-fetal transfusion syndrome

1.3.4.1 Do not monitor for feto-fetal transfusion syndrome in the first trimester.

1.3.4.2 Start diagnostic monitoring with ultrasound for feto-fetal transfusion syndrome (including to identify membrane folding) from 16 weeks. Repeat monitoring fortnightly until 24 weeks.

1.3.4.3 Carry out weekly monitoring of twin and triplet pregnancies with membrane folding or other possible early signs of feto-fetal transfusion syndrome (specifically, pregnancies with intertwin membrane infolding and amniotic fluid discordance) to allow time to intervene if needed.

1.3.5 Monitoring for intrauterine growth restriction

1.3.5.1 Do not use abdominal palpation or symphysis–fundal height measurements to predict intrauterine growth restriction in twin or triplet pregnancies.

1.3.5.2 Estimate fetal weight discordance using two or more biometric parameters at each ultrasound scan from 20 weeks. Aim to undertake scans at intervals of less than 28 days. Consider a 25% or greater difference in size between twins or triplets as a clinically important indicator of intrauterine growth restriction and offer referral to a tertiary level fetal medicine centre.

1.3.5.3 Do not use umbilical artery Doppler ultrasound to monitor for intrauterine growth restriction or birthweight differences in twin or triplet pregnancies.

1.4 Maternal complications

1.4.1 Hypertension

1.4.1.1 Measure blood pressure and test urine for proteinuria to screen for hypertensive disorders at each antenatal appointment in twin and triplet pregnancies as in routine antenatal care[4].

1.4.1.2 Advise women with twin and triplet pregnancies that they should take 75 mg of aspirin[10] daily from 12 weeks until the birth of the babies if they have one or more of the following risk factors for hypertension:

  • first pregnancy

  • age 40 years or older

  • pregnancy interval of more than 10 years

  • BMI of 35 kg/m2 or more at first visit

  • family history of pre-eclampsia.

1.5 Preterm birth

1.5.1 Predicting the risk of preterm birth

1.5.1.1 Be aware that women with twin pregnancies have a higher risk of spontaneous preterm birth if they have had a spontaneous preterm birth in a previous singleton pregnancy.

1.5.1.2 Do not use fetal fibronectin testing alone to predict the risk of spontaneous preterm birth in twin or triplet pregnancies.

1.5.1.3 Do not use home uterine activity monitoring to predict the risk of spontaneous preterm birth in twin or triplet pregnancies.

1.5.1.4 Do not use cervical length (with or without fetal fibronectin) routinely to predict the risk of spontaneous preterm birth in twin or triplet pregnancies.

1.5.2 Preventing preterm birth

1.5.2.1 Do not use the following interventions (alone or in combination) routinely to prevent spontaneous preterm birth in twin or triplet pregnancies:

  • bed rest at home or in hospital

  • intramuscular or vaginal progesterone

  • cervical cerclage

  • oral tocolytics.

1.5.3 Untargeted corticosteroids

1.5.3.1 Inform women with twin and triplet pregnancies of their increased risk of preterm birth and about the benefits of targeted corticosteroids.

1.5.3.2 Do not use single or multiple untargeted (routine) courses of corticosteroids in twin or triplet pregnancies. Inform women that there is no benefit in using untargeted administration of corticosteroids.

1.6 Indications for referral to a tertiary level fetal medicine centre

1.6.1.1 Seek a consultant opinion from a tertiary level fetal medicine centre for:

  • monochorionic monoamniotic twin pregnancies

  • monochorionic monoamniotic triplet pregnancies

  • monochorionic diamniotic triplet pregnancies

  • dichorionic diamniotic triplet pregnancies

  • pregnancies complicated by any of the following:

    • discordant fetal growth

    • fetal anomaly

    • discordant fetal death

    • feto-fetal transfusion syndrome.

1.7 Timing of birth

1.7.1.1 Discuss with women with twin and triplet pregnancies the timing of birth and possible modes of delivery[6] early in the third trimester.

1.7.1.2 Inform women with twin pregnancies that about 60% of twin pregnancies result in spontaneous birth before 37 weeks 0 days.

1.7.1.3 Inform women with triplet pregnancies that about 75% of triplet pregnancies result in spontaneous birth before 35 weeks 0 days.

1.7.1.4 Inform women with twin and triplet pregnancies that spontaneous preterm birth and elective preterm birth are associated with an increased risk of admission to a special care baby unit.

1.7.1.5 Inform women with uncomplicated monochorionic twin pregnancies that elective birth from 36 weeks 0 days does not appear to be associated with an increased risk of serious adverse outcomes, and that continuing uncomplicated twin pregnancies beyond 38 weeks 0 days increases the risk of fetal death.

1.7.1.6 Inform women with uncomplicated dichorionic twin pregnancies that elective birth from 37 weeks 0 days does not appear to be associated with an increased risk of serious adverse outcomes, and that continuing uncomplicated twin pregnancies beyond 38 weeks 0 days increases the risk of fetal death.

1.7.1.7 Inform women with triplet pregnancies that continuing uncomplicated triplet pregnancies beyond 36 weeks 0 days increases the risk of fetal death.

1.7.1.8 Offer women with uncomplicated:

  • monochorionic twin pregnancies elective birth[6]from 36 weeks 0 days, after a course of antenatal corticosteroids has been offered

  • dichorionic twin pregnancies elective birth[6] from 37 weeks 0 days

  • triplet pregnancies elective birth[6] from 35 weeks 0 days, after a course of antenatal corticosteroids has been offered.

1.7.1.9 For women who decline elective birth, offer weekly appointments with the specialist obstetrician. At each appointment offer an ultrasound scan, and perform weekly biophysical profile assessments and fortnightly fetal growth scans.



[3] 'Antenatal care' (NICE clinical guideline 62) recommends determination of gestational age from 10 weeks 0 days. However, the aim in this recommendation is to keep to a minimum the number of scan appointments that women need to attend within a short time, especially if it is already known that a woman has a twin or triplet pregnancy.

[4] See 'Antenatal care' (NICE clinical guideline 62).

[5] This is in addition to the test for anaemia at the routine booking appointment; see 'Antenatal care' (NICE clinical guideline 62).

[6] Specific recommendations about mode of delivery are outside the scope of this guideline.

[7] See appendix D for recommendations 1.2.3.5 to 1.2.3.8 in table form.

[9] See 'Antenatal care' (NICE clinical guideline 62) and also FASP.

[10] At the time of publication (September 2011) this drug did not have UK marketing authorisation for this indication. Informed consent should be obtained and documented. [This recommendation is adapted from recommendation 1.1.2.2 in 'Hypertension in pregnancy' NICE clinical guideline 107.]

  • National Institute for Health and Care Excellence (NICE)