Winter link to pregnancy problems

The time of year could influence pregnancy risks

Women who give birth during the winter are the most likely to have suffered potentially dangerous complications in the preceding months.

Norwegian scientists looked at more than 1.8m births between 1967 and 1998 for cases of pre-eclampsia, a blood pressure problem which can develop to threaten mother and unborn child.

They found that mothers of children born in August had the lowest risk of pre-eclampsia.

What research of this nature does is point other researchers in the right direction so they can investigate the right things

Professor Deirdre Murphy, University of Bristol

However, those who gave birth in the winter months, the risk was higher, particularly in December, when the risk was increased by between 20% and 30%.

The research was published in the British Journal of Obstetrics and Gynaecology on Monday.

Researchers are hopeful that it will give clues to the origins of this condition, which remain little-understood by scientists.

Diet and temperature

However the research team from the National Institute of Public Health in Oslo say there are wide range of possible explanations for the seasonal fluctuation.

They write: "Dietary intake and risk of infection varies with season.

"Also ambient temperature and the amount of daylight can show relatively large seasonal variations, particularly in Nordic countries."

Earlier studies have also linked seasonal changes to the illness.

In Ghana, more cases of eclampsia - the more advanced and potentially dangerous form of the disease - happen in the rainy season.

Seasonal patterns have also emerged in studies in Singapore, Zimbabwe and Sweden, but the Norway study is the largest to date.

Help for the future

Dr Deirdre Murphy, a senior lecturer in maternal medicine at the University of Bristol, told BBC News Online: "We know an awful lot about the management of pre-eclampsia once it is diagnosed, but not very much at all about why it develops in the first place.

"People have suggested there may be a genetic link, or have linked it to damage caused by chemicals in the body called 'free radicals', but there is no proof.

"What research of this nature does is point other researchers in the right direction so they can investigate the right things."

She said that similar research linking a particular type of lymphoma cancer to seasons eventually helped scientists identify a virus to which it appeared to be linked.

Pre-eclampsia is caused by a defect in the placenta, which joins mother and baby and supplies the baby with nutrients and oxygen from the mother's blood.

It often starts in the latter stages of pregnancy.

It is characterised by high blood pressure, but it may be symptomless in its early stages.

However warning signs can be picked up through routine ante-natal checks.

In its more advanced stages, mothers may experience severe headaches, vomiting and vision problems.

It is treatable, often with a combination of drugs and bed-rest, although if it cannot be controlled, the baby may have to be delivered prematurely.

If it is allowed to continue untreated, it may develop into full-blown eclampsia, which can lead to convulsions and put the health of mother and baby at serious risk.