Eating a diet rich in vegetables and fish is associated with a lower risk of a woman developing high blood pressure, and a related condition known as pre-eclampsia, during pregnancy, suggests a large study published in BJOG: An International Journal of Obstetrics and Gynaecology.
The results also show that a Western diet – high in potatoes, meat, white bread and margarine – increase the odds of developing these conditions during pregnancy.
The authors of the study say the findings support women who are at risk of developing these conditions and planning to conceive, or are already pregnant, to eat a well-balanced healthy diet to reduce their risk.
High blood pressure, also known as hypertension, affects around 1 in 10 pregnancies. There are different types of hypertensive disorders that occur during pregnancy. The most common are pre-existing high blood pressure, hypertension that develops during pregnancy (gestational hypertension) and pre-eclampsia which affects 2-8 in 100 women and develops from around 20 weeks of gestation.
In a bid to find out about the role of a mother’s diet in the risk of high blood pressure and pre-eclampsia, a team of researchers carried out a large study of the dietary habits of pregnant women and their associated risks of these conditions.
The study involved 55,138 women who took part in the Danish National Birth Cohort.
Women took part in two telephone interviews during pregnancy, at 12 and 30 weeks of gestation and in two interviews at six and 18 months after birth. A questionnaire assessed dietary intake at 25 weeks of gestation.
The results show that a diet rich in vegetables and fish decreased the odds of developing gestational hypertension by 14% (5491/39,362 women developed hypertension) and pre-eclampsia by 21% (1168/54,778 women developed pre-eclampsia).
Meanwhile, a Western diet increased the odds of developing gestational hypertension by 18% (5491/39,362 women developed hypertension) and pre-eclampsia by 40% (1168/54,778 women developed pre-eclampsia).
In total, 14% of women had gestational hypertension, 2% had pre-eclampsia and 0.4% had severe pre-eclampsia. On average, women with high blood pressure or pre-eclampsia had a higher body mass index (1.6-2.3 kg/m2 higher) than those without the conditions.
While the study shows only an association between diet and risk of hypertension during pregnancy, the results add to an existing body of evidence that supports the consumption of a healthy, well-balanced diet.
Ms Emmanuella Ikem, School of Medicine, University of Bristol, and School of Public Health, Imperial College London and author of the BJOG study, said:
“Our findings support the importance of eating a healthy and well-balanced diet in vegetables and fish and cutting out processed foods where possible. This will help to reduce a woman’s risk of developing high blood pressure and pre-eclampsia during pregnancy.
“Current advice recommends eating at least five portions of different fruit and vegetables every day, instead of foods high in fat. And generally it is safe to consume fish during pregnancy – no more than two portions of oily fish, such as mackerel or salmon, a week, and no more than two fresh tuna steaks or four medium-sized cans of tuna a week. Women should avoid eating shark, swordfish or marlin.”
Dr Pat O’Brien, Consultant Obstetrician and Spokesperson for the Royal College of Obstetricians and Gynaecologists, said:
“High blood pressure and pre-eclampsia can result in harmful complications for mother and baby. These conditions must be managed with medications and monitored closely by healthcare professionals during pregnancy and birth.
"These latest findings are encouraging as it shows there are additional steps a woman can take to reduce her risk of these conditions by eating healthily. It is also vital that women and their partners are encouraged to manage their weight and to have a healthy diet ideally before conception, to ensure the healthiest possible pregnancy and best start to their child’s life.”
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NHS Choices on managing hypertension during pregnancy
NICE guidance on managing hypertension during pregnancy
RCOG recommends the following nutritional advice for women who are pregnant:
• Eat at least five portions of different fruit and vegetables every day rather than foods high in fat and calories. Potatoes do not count towards the five-a-day target.
• Base your meals on starchy foods such as potatoes, bread, rice and pasta, choosing wholegrain if possible.
• Eat a low-fat diet and don’t increase the number of calories you eat. Eat as little fried food as possible and avoid drinks that are high in added sugars, and other foods such as sweets, cakes and biscuits that have a high fat or sugar content.
• Instead, eat fibre-rich foods such as oats, beans, lentils, grains and seeds, as well as wholegrain bread, brown rice and wholemeal pasta.
• Eat some protein every day; choose lean meat, and try to eat two portions of fish a week. Lentils, beans and tofu are also a good source of protein.
• Watch the portion size of your meals and snacks and note how often you eat. Do not ‘eat for two’.
• Always eat breakfast.
In general, eating fish is a healthy option during pregnancy, but the current advice from the Department of Health is to eat no more than two portions of oily fish, such as mackerel or salmon, a week. This is because too much of a substance found in oily fish (mercury) can be harmful to an unborn baby’s development. Also, pregnant women should not eat more than two fresh tuna steaks or four medium-sized cans of tuna a week, and should avoid eating shark, swordfish or marlin.
RCOG information on healthy eating during pregnancy
The RCOG, in partnership with Tommy’s, Public Health England and the UCL Institute for Women’s Health has launch of a new digital tool, Planning for Pregnancy. The innovative tool provides tailored information for women on how they can prepare before conception in order to have a healthy pregnancy.
BJOG: An International Journal of Obstetrics and Gynaecology is owned by the Royal College of Obstetricians and Gynaecologists (RCOG) but is editorially independent and published monthly by Wiley. The journal features original, peer-reviewed, high-quality medical research in all areas of obstetrics and gynaecology worldwide. Please quote ‘BJOG’ or ‘BJOG: An International Journal of Obstetrics and Gynaecology’ when referring to the journal. To keep up to date with our latest papers, follow @BJOGTweets.
About the RCOG
The Royal College of Obstetricians and Gynaecologists is a medical charity that champions the provision of high quality women’s healthcare in the UK and beyond. It is dedicated to encouraging the study and advancing the science and practice of obstetrics and gynaecology. It does this through postgraduate medical education and training and the publication of clinical guidelines and reports on aspects of the specialty and service provision.