- early diagnosis is essential
- supplementation of iron and folic acid
- regular monitoring of haemoglobin levels
- increased level of review in antenatal clinic
- booking of the birth into a specialist unit
NICE have given guidance regarding the diagnosis and assessment of multiple pregnancies (1)
Determining gestational age and chorionicity
- offer women with a twin or triplet pregnancy a first trimester ultrasound scan to estimate gestational age and determine chorionicity and amnionicity (ideally, these should all be performed at the same scan
- chorionicity
- number of chorionic (outer) membranes that surround babies in a multiple pregnancy. If there is only 1 membrane, the pregnancy is described as monochorionic; if there are 2, the pregnancy is dichorionic; and if there are 3, the pregnancy is trichorionic. Monochorionic twin pregnancies and monochorionic or dichorionic triplet pregnancies carry higher risks because babies share a placenta
- amniocity
- number of amnions (inner membranes) that surround babies in a multiple pregnancy. Pregnancies with 1 amnion (so that all babies share an amniotic sac) are described as monoamniotic; pregnancies with 2 amnions are diamniotic; and pregnancies with 3 amnions are triamniotic
- determine chorionicity and amnionicity at the time of detecting a twin or triplet pregnancy by ultrasound using:
- the number of placental masses
- the presence of amniotic membrane(s) and membrane thickness
- the lambda or T-sign.
- 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
- if a woman with a twin or triplet pregnancy presents after 14+0 weeks, determine chorionicity and amnionicity at the earliest opportunity by ultrasound using all of the following:
- the number of placental masses
- the presence of amniotic membrane(s) and membrane thickness
- the lambda or T-sign
- discordant fetal sex
- If it is not possible to determine chorionicity or amnionicity by ultrasound at the time of detecting the twin or triplet pregnancy, seek a second opinion from a senior sonographer or refer the woman to a healthcare professional who is competent in determining chorionicity and amnionicity by ultrasound scan as soon as possible
- if it is difficult to determine chorionicity, even after referral (for example, because the woman has booked late in pregnancy), manage the pregnancy as a monochorionic pregnancy until proven otherwise
- 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.
Monitoring for intrauterine growth restriction
- at each ultrasound scan from 24 weeks, offer women with a dichorionic twin or trichorionic triplet pregnancy diagnostic monitoring for fetal weight discordance using 2 or more biometric parameters and amniotic fluid levels. To assess amniotic fluid levels, measure the deepest vertical pocket (DVP) on either side of the amniotic membraneestimate fetal weight discordance using two or more biometric parameters
- continue monitoring for fetal weight discordance at intervals that do not exceed:
- 28 days for women with a dichorionic twin pregnancy
- 14 days for women with a trichorionic triplet pregnancy
- calculate and document estimated fetal weight (EFW) discordance for dichorionic twins using the formula below:
- ([EFW larger fetus − EFW smaller fetus] ÷ EFW larger fetus) × 100
- calculate and document EFW discordance for trichorionic triplets using the formula below:
- ([EFW largest fetus − EFW smallest fetus] ÷ EFW largest fetus) × 100 and
- ([EFW largest fetus − EFW middle fetus] ÷ EFW largest fetus) × 100
- inrease diagnostic monitoring in the second and third trimesters to at least weekly, and include Doppler assessment of the umbilical artery flow for each baby, if:
- there is an EFW discordance of 20% or more and/or
- the EFW of any of the babies is below the 10th centile for gestational age
- refer women with a dichorionic twin or trichorionic triplet pregnancy to a tertiary level fetal medicine centre if there is an EFW discordance of 25% or more and the EFW of any of the babies is below the 10th centile for gestational age because this is a clinically important indicator of selective fetal growth restriction
Screening for structural abnormalities
- offer screening for structural abnormalities (such as cardiac abnormalities) in twin and triplet pregnancies as in routine antenatal care
- 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
- allow 45 minutes for the anomaly scan in twin and triplet pregnancies
- allow 30 minutes for growth scans in twin and triplet pregnancies.
Monitoring for feto-fetal transfusion syndrome
- offer diagnostic monitoring for feto-fetal transfusion syndrome to women with a monochorionic twin or triplet pregnancy. Monitor with ultrasound every 14 days from 16 weeks until birth
- use ultrasound assessment, with a visible amniotic membrane within the measurement image, to monitor for feto-fetal transfusion syndrome. Measure the DVP depths of amniotic fluid on either side of the amniotic membrane
- increase the frequency of diagnostic monitoring for feto-fetal transfusion syndrome in the woman's second and third trimester to at least weekly if there are concerns about differences between the babies' amniotic fluid level (a difference in DVP depth of 4 cm or more). Include Doppler assessment of the umbilical artery flow for each baby
- refer the woman to a tertiary level fetal medicine centre if feto-fetal transfusion syndrome is diagnosed, based on the following:
- the amniotic sac of 1 baby has a DVP depth of less than 2 cm and
- the amniotic sac of another baby has a DVP depth of:
- over 8 cm before 20+0 weeks of pregnancy or
- over 10 cm from 20+0 weeks
- refer the woman to her named specialist obstetrician for multiple pregnancy in her second or third trimester for further assessment and monitoring if:
- the amniotic sac of 1 baby has a DVP depth in the normal range and
- the amniotic sac of another baby has a DVP depth of:
- less than 2 cm or
- 8 cm or more
NICE have issued guidance regarding the timing of birth if multiple pregnancy (1):
- explain to women with a twin pregnancy that about 60 in 100 twin pregnancies result in spontaneous birth before 37 weeks
- explain to women with a triplet pregnancy that about 75 in 100 triplet pregnancies result in spontaneous birth before 35 weeks
- explain to women with a twin or triplet pregnancy that spontaneous preterm birth and planned preterm birth are associated with an increased risk of admission to a neonatal unit
- explain to women with an uncomplicated dichorionic diamniotic twin pregnancy that:
- planned birth from 37+0 weeks does not appear to be associated with an increased risk of serious neonatal adverse outcomes and
- continuing the pregnancy beyond 37+6 weeks increases the risk of fetal death
- explain to women with an uncomplicated monochorionic diamniotic twin pregnancy that:
- planned birth from 36+0 weeks does not appear to be associated with an increased risk of serious neonatal adverse outcomes and
- continuing the pregnancy beyond 36+6 weeks increases the risk of fetal death
- explain to women with an uncomplicated monochorionic monoamniotic twin pregnancy that planned birth between 32+0 and 33+6 weeks does not appear to be associated with an increased risk of serious neonatal adverse outcomes. Also explain that:
- these babies will usually need to be admitted to the neonatal unit and have an increased risk of respiratory problems
- continuing the pregnancy beyond 33+6 weeks increases the risk of fetal death
- explain to women with an uncomplicated trichorionic triamniotic or dichorionic triamniotic triplet pregnancy that continuing the pregnancy beyond 35+6 weeks increases the risk of fetal death
- explain to women with a monochorionic triamniotic triplet pregnancy or a triplet pregnancy that involves a shared amnion that the timing of birth will be decided and discussed with each woman individually
For full details see NICE (April 2024). Twin and triplet pregnancy
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