Pregnant women are more likely to suffer the heartbreak of a miscarriage during the summer, a study suggests. Researchers behind the eight-year project tracked the pregnancies of 6,000 women in the US.
Miscarriage rates peaked in June, July and August — the traditional summer months in the Northern Hemisphere, analysis showed.
The highest seasonal difference was logged in August, when miscarriage rates were 44 higher than in February.
The trend was strongest for miscarriages that occurred before eight weeks, when a foetus is still the size of a raspberry.
Experts believe extreme heat or lifestyle factors during warmer weather could be to blame — but they said further research is needed.
Researchers behind the eight-year project tracked the pregnancies of 6,000 women in the US. Miscarriage rates peaked in June, July and August — the traditional summer months in the Northern Hemisphere, analysis showed
Dr Amelia Wesselink, study author from Boston University, said: ‘Any time you see seasonal variation in an outcome, it can give you hints about causes of that outcome.
‘We found miscarriage risk, particularly risk of “early” miscarriage before eight weeks of gestation, was highest in the summer.’
She added: ‘Heat is associated with higher risk of other pregnancy outcomes, such as preterm delivery, low birth weight, and stillbirth, in particular.
‘Medical guidance and public health messaging — including heat action plans and climate adaptation policies — need to consider the potential effects of heat on the health of pregnant people and their babies.’
The researchers analysed survey data on women who provided data on pregnancy loss, when it occurred and how far along they were.
The ongoing National Institutes of Health programme, which began in 2013, recruits women trying to conceive and follows monitors them until they give birth.
Published in the journal Epidemiology, the findings show the risk of miscarriage during any week of pregnancy was 31 per cent higher in late August, compared to late February.
Analysis showed rates appeared strongest for women living in Southern and Midwest states, ‘where summers are hottest’ and temperatures can reach 110F (43C).
Exposure to heat could be driving the summer miscarriage trend, which is already linked with preterm delivery, low birth weight and stillbirth, the experts said.
Experts are not sure why heat affects pregnancy, but theories include dehydration among expectant mothers, disruption to the development of the placenta and changes in blood flow to the uterus.
But they noted that too few studies have examined this link so the topic ‘warrants further exploration’.
The team said their findings ‘begin to fill a gap’ on seasonal miscarriage patterns.
Earlier studies relied on clinical or fertility data, which likely overlook miscarriages that occurred early and among those experiencing fertility challenges, they said.
HOW COMMON ARE MISCARRIAGES?
A miscarriage is the loss of a pregnancy during the first 23 weeks.
Vaginal bleeding followed by cramping and pain in the lower abdomen are the most common symptoms.
Many miscarriages go unreported because they are often managed at home. But it is thought one in eight pregnancies end with losing the baby.
Lots more occur before a person is even aware they are pregnant.
Losing three or more pregnancies in a row is uncommon and affects around one per cent of women.
Doctors believe most occur due to abnormal chromosomes in the baby.
In most cases, miscarriage is a one-off event and people go on to have a successful pregnancy in the future.
The majority of miscarriages cannot be prevented. But avoiding smoking, drinking alcohol and using drugs when pregnant lowers the risk.
Being a healthy weight before getting pregnant and eating a healthy diet can also help.
Those suffering a miscarriage are usually referred to hospital for an ultrasound scan.
If one has occurred, it will often pass out naturally in one or two weeks. Sometimes medication is used to assist passing the tissue or minor surgery can be performed.