Updated October 2013

Explaining premature birth - risks and causes

Uterine abnormality - problems with the womb

Some women have a congenital uterine abnormality, which is a womb/uterus that formed in an unusual way before birth.

Depending on the shape of the uterus, the risks of miscarriage or premature birth can be higher in these cases. Uterine abnormality is also linked to cervical insufficiency/incompetence, another factor leading to preterm birth.

Bicornuate (heart-shaped) womb

A bicornuate womb is heart-shaped. Women with a bicornuate womb have no extra difficulties with conception or in early pregnancy, but there is a higher risk of miscarriage and preterm birth. It can also affect the way the baby lies in later pregnancy so a caesarean birth might be recommended. 

Unicornuate womb

Having a unicornuate womb is rare. It means your womb is half the size of a normal womb because one side failed to develop. There is an increased risk of late miscarriage or preterm birth. The baby may lie in an awkward position in later pregnancy so a caesarean birth might be recommended. Women with a unicornuate womb have no extra difficulties with conception.

Didelphic (double) womb

The didelphic womb is split in two, with each side having its own cavity, cervix and vagina. Women with a didelphic womb have no extra difficulties with conception and it is only linked to a small increased risk in premature birth.

Septate/subseptate womb

The septate womb has a wall of muscle coming down the centre splitting the space in two. Sometimes the wall only comes part-way down the womb (subseptate) and other times it comes the whole way down. Women with subseptate or septate wombs are more likely to have difficulties with conception. There is also an increased risk of first-trimester miscarriage and preterm birth. In later pregnancy the baby may lie in an awkward position.

Arcuate womb

The arcuate womb looks very like a normal womb but it has a dip at the top. Arcuate womb does not increase your risk of preterm birth or first trimester miscarriage but it does increase your risk of second trimester miscarriage. In later pregnancy your baby may lie in an awkward position so you may need to have a caesarean birth.

How will I know if I have abnormal womb?

There are unlikely to be any physical symptoms in early pregnancy.

If you have a didelphic (double) womb or a unicornuate womb it may be spotted in your routine scans as it looks very different from a normal womb. In other cases, especially if the abnormality is not severe, it is unlikely to be picked up as routine pregnancy scans do not specifically look for this.

If you have had recurrent first-trimester miscarriages (three or more) or one or more second trimester miscarriages an abnormally-shaped womb will be suspected. A pelvic ultrasound or MRI scan or laparoscopy may be offered to look at your uterus to see the shape.

What is the treatment for uterine abnormalities?

Operating on the womb is not normally performed because it is linked to later infertility and carries a risk of any scar opening during the pregnancy.

Once you have been diagnosed as having an abnormally-shaped womb you will be put into the care of an obstetric team and you will have extra scans and hospital visits to check up on you and your baby throughout the pregnancy.

If your baby ends up in an awkward position (upside-down or bottom first for example) in later pregnancy you will be offered a caesarean section.


Sources

J David, Steer P et al (2010) High risk pregnancy, management options, Elsevier Saunders

Chan YY, Jayaprakasan K et al (2011), Reproductive outcomes in women with congenital uterine anomalies: a systematic review. Ultrasound Obstet Gynecol, 38: 371–382. doi: 10.1002/uog.10056

RCOG (2011) Recurrent Miscarriage, Investigation and Treatment of Couples, Green-top Guideline 17, Royal College of Obstetricians and Gynaecologists 


The causes and problems of premature birth

Your premature baby:

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