Twin Pregnancy Complications

What this page is, and is not

Pre-eclampsia, fetal growth restriction and preterm labour all have general accounts that apply to any pregnancy, and those accounts are not repeated here. This page is about the differences: what changes in screening, thresholds, medication and timing specifically because there is more than one baby. If you want the general picture of each condition, read that first — this is the twin overlay.

Two framing points from the sources. Twins Trust says most people with a multiple pregnancy do not experience serious complications, but that the risks are higher than in a single pregnancy, so care is more frequent and more detailed. RCOG notes that monochorionic and dichorionic twin pregnancies share increased risks of preterm birth, fetal growth restriction, pre-eclampsia, maternal pregnancy symptoms and postpartum haemorrhage — the shared placenta adds a further set on top.

Pre-eclampsia: more often, earlier, more severe

ACOG states the difference in one sentence: pre-eclampsia "occurs more often in multiple pregnancies than in singleton pregnancies. It also tends to occur earlier and is more severe in multiple pregnancies." Those three modifiers — more often, earlier, more severe — are the whole reason twin surveillance is structured the way it is.

NICE asks for blood pressure and urine testing for proteinuria at every antenatal appointment in a twin or triplet pregnancy. Because twin schedules include more appointments — at least eight for dichorionic and eleven for monochorionic twins — you are screened more often as a direct consequence of the scan calendar.

Aspirin is where people most often assume more than the guideline says. NICE NG137 advises low-dose aspirin daily from 12 weeks until birth for women with a twin or triplet pregnancy who have two or more of the risk factors listed in the NICE hypertension in pregnancy guideline, and notes that in September 2019 this was an off-label use. Tommy's frames it the same way. A twin pregnancy alone does not automatically trigger it under NG137, which is worth clarifying with your team rather than assuming either way.

Growth restriction: measured by comparison, not by tape measure

This is the most concrete difference. NICE says explicitly not to use abdominal palpation or symphysis–fundal height measurements to monitor for growth restriction in dichorionic or monochorionic twin pregnancies. Instead it asks for ultrasound at defined intervals, using two or more biometric parameters plus amniotic fluid, and for estimated fetal weight discordance to be calculated and documented at each scan.

The intervals differ by chorionicity: from 24 weeks with gaps not exceeding 28 days for dichorionic twins, and from 16 weeks with gaps not exceeding 14 days for monochorionic twins. The thresholds are the same for both — weekly monitoring with umbilical artery Doppler at 20% discordance or any baby below the 10th centile, and referral to a tertiary fetal medicine centre at 25% discordance together with a baby below the 10th centile.

ACOG makes a point worth holding onto: discordant growth "is common with multiples. It does not always signal a problem." The measurement exists to find the cases that do.

Preterm labour: screened for by default

In a singleton pregnancy, cervical length screening is generally targeted at those with risk factors. In a twin pregnancy it is not. Since its 2024 update NICE recommends offering a single cervical length scan between 16 and 20 weeks to everyone with a twin or triplet pregnancy, and offering progesterone 200 mg vaginal capsules once a day at bedtime if the cervix measures 25 mm or less, continued until 34 weeks or birth if sooner. The same offer applies if a short cervix turns up incidentally on a scan between 20 and 24 weeks.

NICE is equally clear about what not to do. It says do not offer intramuscular progesterone, and do not routinely offer an arabin pessary, bed rest, cervical cerclage or oral tocolytics — alone or in combination — to prevent spontaneous preterm birth in twin or triplet pregnancy. It also says not to use fetal fibronectin testing alone, or home uterine activity monitoring, to predict the risk.

On steroids, NICE says to inform women of their increased risk of preterm birth and the benefits of targeted corticosteroids, but not to use single or multiple untargeted routine courses, adding that there is no benefit in untargeted administration.

Anaemia, gestational diabetes and bleeding

NICE adds a full blood count at 20 to 24 weeks, on top of the booking test, specifically because anaemia is more common in twin and triplet pregnancy, with a repeat at 28 weeks. Tommy's explains the cause as a shortage of iron because the developing babies need a lot of it, and lists the same three testing points.

ACOG says women carrying multiples have a high risk of gestational diabetes, which can in turn increase the risk of pre-eclampsia. Twins Trust lists high blood pressure, pre-eclampsia and gestational diabetes together as the conditions that make attending every appointment worthwhile even when you feel fine.

For bleeding after birth, NICE says to start assessing the risk of postpartum haemorrhage in the antenatal period and continue through labour, to offer an individualised risk assessment explaining that multiple pregnancy is itself a risk factor for increased blood loss, and to offer active rather than physiological management of the third stage. It asks for intravenous access and a group and save at the start of established labour.

Tommy's adds that the risk of deep vein thrombosis in pregnancy is higher with multiple babies, while noting that venous thrombosis remains uncommon overall in pregnancy or in the first six weeks after birth, occurring in 1 to 2 in 1,000 women.

The complications that only exist with a shared placenta

Three conditions have no singleton equivalent at all, and they only occur where babies share a placenta: twin-to-twin transfusion syndrome, twin anaemia polycythaemia sequence, and twin reversed arterial perfusion sequence. NICE also lists conjoined twins, discordant fetal death and fetal anomaly among the reasons to seek a tertiary fetal medicine opinion.

These are covered in detail on their own pages. The point to carry into this one is that they are found by ultrasound and by nothing else — no blood test, blood pressure reading or symptom check will pick them up, which is why the monochorionic scan schedule is as intensive as it is.

Loss of one baby

Tommy's addresses this directly, noting that multiple pregnancies carry a higher chance of loss, which may follow chromosomal problems, complications of a shared placenta such as TTTS, or selective growth restriction. It also names the early form — sometimes called disappearing twin syndrome, where one baby stops developing in the first trimester — and says that even though it happens early, it can still be a very painful loss. Both Tommy's and Twins Trust run bereavement support for families in this position.

When to ring rather than wait

The urgent symptom list is not twin-specific, and the HSE's warning signs guidance sets out the standard version for any pregnancy: severe headache, vision changes, sudden swelling, pain under the ribs, bleeding, reduced movements, fluid loss, or feeling generally unwell. What differs in a twin pregnancy is the prior probability. With pre-eclampsia occurring more often and earlier, and with TTTS able to progress between fortnightly scans, the threshold for making the call should be lower, not higher.

Twins Trust puts it as well as anyone: you are the expert on your own body, and if something does not feel right you should contact your midwife, triage line or consultant even if it is not on a list of typical warning signs.