New Zealand Multiple Birth Association

Pregnancy complications

Twin pregnancies have increased risks for both the mother and the babies. There is an increased risk of anaemia, vaginal bleeding, gestational diabetes mellitus (GDM) and pre-eclampsia—which occur in singleton pregnancies, but are more common in twin pregnancies. The most common complication in multiple pregnancy is the risk of premature labour and pre-term birth—this is covered in the following section.


Iron-deficiency anaemia affects 10-15% of pregnant women, and women with multiple pregnancy are at greater risk, as each subsequent baby puts extra strain on the mother’s iron intake. The mother’s body will prioritise the babies’ iron needs ahead of her own—this is good news, as it means that although the mother might be anaemic, her babies should still be getting sufficient iron. Although anaemia can cause serious problems, there is little risk to the babies unless the mother is severely anaemic.

It is routine to test for iron-deficiency anaemia during pregnancy. Pregnant women often appear to have low haemoglobin levels, as there is extra fluid in the blood during pregnancy, which dilutes the red blood cells. Only if your levels are seriously low, will it be considered cause for concern. Be sure to inform your LMC if you have an infection, though, as an infection will mean you test higher for haemoglobin levels, which may result in an under-diagnosis of iron deficiency. Also inform your LMC if you are a vegetarian or vegan.

When a woman is suspected of being iron deficient during pregnancy, a full iron blood screen should be conducted, and treatment initiated and followed-up. Following birth, a woman who has been iron deficient during pregnancy should have a further follow-up to check if she is still iron deficient. Iron deficiency during breastfeeding should be treated, because low iron status leads to an increased risk of illness, tiredness and breast infections. These can negatively impact on the mother’s ability to care for her infants and may also affect her breastfeeding.

Vaginal bleeding

Up to 10% of all women have bleeding during their pregnancy. This is more common with twins. Bleeding during the first trimester is common, usually as a result of implantation bleeding. It could, however, also be the result of a miscarriage or ectopic pregnancy. Bleeding in the second and/or third trimesters could indicate: a problem with the cervix; placental abruption; placenta praevia; preterm labour; or, miscarriage. If you have any bleeding during pregnancy, it is best to contact your LMC or specialist, especially if the bleeding is also accompanied by cramps or abdominal pains. It can be useful to wear a pad, so that you can determine how much you are bleeding. Never use a tampon during pregnancy. It may also be useful to discuss with your LMC or specialist, whether to avoid sexual intercourse during your pregnancy.

Gestational diabetes mellitus (GDM)

Gestational diabetes affects 2-3% of all pregnant women. In most cases, it is a temporary form of diabetes, brought on by the body’s inability to produce enough insulin during pregnancy. Screening for gestational diabetes is generally offered when a woman is   between 24 and 28 weeks gestation. This is normally done through a blood test with the results indicating whether gestational diabetes is a potential problem. If you are concerned or have a family history of GDM, discuss this with your specialist.


Pre-eclampsia is also known as Toxaemia and Pregnancy-Induced Hypertension (PIH), and affects around 3-8% of all pregnant women—about 1 in 3 mothers pregnant with twins will develop it.

The signs of pre-eclampsia are high blood-pressure and protein in the urine. It only occurs during pregnancy, usually after 20 weeks gestation, but rarely before 32 weeks. Often women diagnosed with pre-eclampsia feel fine, but some of the signs and symptoms can include swelling (oedema) of the face or hands, sudden weight gain, headaches and changes in vision. If left untreated, pre-eclampsia can be life-threatening.

The only remedy for pre-eclampsia is delivery of the babies. The specialist will balance the risk to the babies of being born prematurely, against the risk to the mother from pre-eclampsia. If pre-eclampsia develops too early in the pregnancy for the babies to be delivered safely, the pre-eclampsia will likely be managed by having the mother on full-time bed-rest, possibly in hospital. Sometimes medication to lower the mother’s blood pressure will be administered. Usually, pre-eclampsia goes away after the babies are born, as the mother’s blood pressure gradually reduces.

Premature labour and preterm birth

Preterm birth generally occurs in 7-10% of all births—for twin births this rises to 50%, of which 20% are less than 34 weeks, and 6-7% are less than 32 weeks gestation. Mothers of multiples are more likely to experience per-term labour because between 29 and 32 weeks gestation, the uterus is the same size as a full term singleton pregnancy. Babies born before 36 weeks are considered pre-term. Babies born after 26 weeks have a good chance of survival.

Signs and symptoms of premature labour

When pregnant with multiples, it is vital to know some of the signs and symptoms that might indicate that labour is starting because the risk of preterm labour and birth are higher. It is not always easy to know if you are experiencing premature labour, as often the signs and symptoms are very subtle—you may just feel that something is not right. Here are a few signals to watch out for:

  • Dull low back ache—this pain might be continuous or intermittent, it will not be related to posture, and might branch out to your front or sides
  • Rhythmic or persistent pelvic pressure (feels like the babies are pushing down)—you may experience this pain in your back or thighs
  • Abdominal cramping, with or without diarrhoea (like period cramps)
  • Diarrhoea, gas pains, or intestinal discomfort
  • An increase or change in vaginal discharge (blood, water or mucus)
  • Tightening across your abdomen—this may be painless and are often called Braxton-Hicks contractions; they generally ease with rest but if they become frequent and prolonged you should seek advice
  • Feeling ‘bad’
  • A ‘heavy’ feeling.

It is always best to get discuss these signs and symptoms with your maternity care provider (LMC or specialist) and ask for a physical assessment. It is better to be checked earlier than later, just to be on the safe side—don’t wait for the symptoms to go away!

If you have any of the following, contact your LMC/specialist and/or the hospital maternity unit and prepare to go to the maternity unit/birthing suite immediately:

  • Water leaking or gushing from the vagina
  • A show (a white or pink mucus discharge)
  • Bleeding from the vagina
  • Regular, painful contractions—during a contraction the uterus tightens, becomes hard and then relaxes again
  • If you just feel something is not right—trust your intuition.


For information on strategies to reduce the risk of premature birth, click here.