In twin pregnancy women with a history of polycystic ovarian syndrome (PCOS) are a high-risk group for preterm birth.

Using the comprehensive Swedish medical birth and national patient registers almost 1.5 million births over a 15-year period, between 1995 and 2009, were identified. Of these, 20,965 were twin births of which 223 (1.1%) were to women who had a diagnosis of PCOS.

Women with PCOS were more likely to have a higher early pregnancy BMI (P < 0.0001) and to have used assisted reproductive technology to conceive 31.4% vs 15.0% (P < 0.001). They were also on average older (P = 0.2) and more likely to be non-smokers (P = 0.03).

As can be seen in table 1, below, women with PCOS were more likely to have a preterm birth, adjusted risk ratio (RR) 1.16 (95% CI: 0.99-1.35) particularly a very preterm birth, adjusted RR 1.51 (95% CI: 0.99-2.3), compared with women without PCOS, a significant proportion of which followed spontaneous preterm delivery.

Caesarean section rates did not differ between the groups although birthweight for babies to PCOS women was on average lower.

After controlling for preterm delivery this difference disappeared.

There were no significant differences between the groups in pre-eclampsia, low Apgar scores or perinatal mortality.

This study has shown that in twin pregnancy women with a history of PCOS are a high-risk group for preterm birth.

Even after controlling for confounding variables the authors considered that a ‘PCOS factor’ remained. This may be due to hyperandrogenism, disturbed glucose/insulin metabolism and an inflammatory state: all more commonly seen in women with PCOS. Indeed PCOS is considered by some to be the ovarian manifestation of the metabolic syndrome.

The population incidence of PCOS is estimated to be 5-15%. Because so few women in this study were identified with PCOS (1.1%) the findings presented here may well have underestimated the ‘PCOS factor’.

Dr Chris Barclay