Study reveals twin weight risks

THERE is an increased risk of death in a twin pregnancy if the difference in weight between the two babies is more than 20%, an all-Ireland study reveals.

It found a difference of 18% or more in twin birth weights is associated with an increased risk of foetal or neonatal death, bowel complications, breathing difficulties and infections.

Twins who shared a single placenta were found to be at the highest risks and the larger twin faced the same chance of death as his or her smaller co-twin.

The study of 1,001 women with twin pregnancies between 2007 and 2009 was led by Perinatal Ireland and the Royal College of Surgeons in Ireland (RCSI) and funded by the Health Research Board.

Consultant obstetrician, Dr Fionnuala Breathnach, said the degree of weight difference that should be considered abnormal had always been a matter of debate. “Our goal was to accurately define the difference in twin weights that translates into an increased risk of complications,” she said.

She said the 18% cut-off point that emerged from the study represented that threshold above which risks increased for both babies.

“We tend to think of the smaller twin as being the more vulnerable one, yet our study demonstrates that the larger twin of a discordant pair is equally at risk,” she said.

Dr Breathnach said recognition of the threshold difference in weight during pregnancy should trigger closer foetal monitoring and, in some circumstances, might prompt early delivery.

The study also found that 77% of natural twin labour births overseen by an obstetrician were successful and infant death rates were no different from those following a planned caesarean twin delivery.

While it is considered that the first twin must be “head down” to allow natural labour, the research found that the position of the second twin before labour did not influence whether labour successfully resulted in a normal birth of both twins.

In 4% of cases, the mother underwent a normal birth of the first twin, followed by a caesarean delivery of the second baby, a figure lower than the international rate.

Dr Breathnach said that how best to deliver twins was a contentious issue internationally. “It is important to acknowledge that in more than half of twin pregnancies in this study delivery was by caesarean section without any attempt at labour.”

She said the study demonstrated that, under appropriate conditions and with careful patient selection, a high prospect of successful and safe vaginal delivery could be achieved with natural labour.

Dr Breathnach said the study also revealed a very low rate of infant mortality around the time of birth.

“It is not entirely clear to what these impressive results should be attributed but, to me, it is in no small part due to the high standards of excellence in obstetric care for which Ireland has gained an international reputation,” she said.

The research will be published this week in the US Journal, Obstetrics and Gynaecology.