Reviewed April 2014, next review April 2017

Explaining premature birth - risks and causes

Multiple pregnancy and premature birth

Multiple pregnancy means carrying more than one baby, normally twins.

Multiple pregnancies are getting more common because they are linked to infertility treatments, which are becoming more available. The most common multiple is twins. 

Twins can be monozygotic (one fertilised egg splits in two) or dizygotic (two eggs are fertilised). Monozygotic twins will normally be the same sex. Infertility treatments are linked to dizygotic twins.

Most women who are pregnant with twins deliver healthy babies but carrying more than one baby increases the health risks for the mother and baby.

Multiple pregnancy is normally spotted in routine pregnancy scans and most women know by 20 weeks that they are carrying more than one baby.

Premature birth

Carrying more than one baby means you are more likely to have a premature delivery.

The average gestation for multiples is:

  • Twins: 37 weeks
  • Triplets: 34 weeks
  • Quadruplets: 32 weeks

If the baby is not born by then, most twin pregnancies are induced by 38 weeks because the health risks increase after that.

Read more about gestational age of delivery and medical needs.

What are the risks and complications of multiple pregnancy

Most women with twins stay healthy through the pregnancy and deliver healthy babies. However, you will be at higher risk of some of the potential complications that can cause premature birth or lead to induction, including:

What treatment can I expect if I have a multiple pregnancy?

Multiple pregnancies are considered high risk so you will be put into the care of a special team of obstetricians and specialist midwives who will monitor your pregnancy and baby carefully for the problems above.

The delivery, vaginal or caesarean, will depend on the position of your babies. There will be a specialist team present at the birth in case of complications. It will include midwives, obstetricians, anaesthetists and paediatricians.


Macdonald S (2012) Mayes Midwifery, Fourteenth Edition, Balliere Tindall Elseviere

Norman J, Greer I (2011) Preterm labour, managing risk in clinical practice, Cambridge University Press

NICE (2011) CG129 Multiple pregnancy: full guideline, National Institute of Health and Clinical Excellence


The causes and problems of premature birth

Your premature baby:

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The average length of pregnancy for women expecting triplets is 34 weeks.