Nutrition and supplements during pregnancy

IN BPJ 15 (AUGUST 2008), we covered the topic of vitamin and mineral deficiencies. GPs tell us that they would like more information on what supplements or additional foods they should be prescribing or recommending for women who wish to become pregnant or those who are pregnant.

The importance of ensuring good maternal health during pregnancy is widely recognised while an increasing body of evidence suggests that nutritional status prior to pregnancy strongly influences foetal and infant outcomes. In view of this, the goal is to ensure that women attain good nutritional status before, during and between pregnancies to optimise their own health and reduce the risk of pregnancy complications, birth defects and the onset of chronic diseases in their children.

Attention to pre-conception nutrition improves pregnancy outcomes

Improving nutritional status before pregnancy is challenging because about half of pregnancies in New Zealand are not planned.^1,2 Even among women planning pregnancy, few seek medical or nutritional advice prior to conception, and most women do not have their first prenatal care visit until well into the first trimester.

Folate reduces risk of neural tube defects

It is well established that folate decreases the risk for neural tube defects. Women planning a pregnancy, or who are in the early stages of pregnancy, are advised to take a daily folic acid supplement of 800 mcg for at least four weeks before, and up to 12 weeks after conception (although women are recommended to continue with this supplement throughout pregnancy). Higher doses (5 mg daily) are recommended for those who have had a previous neural tube defect affected pregnancy, a family history of neural tube defects, or are taking anticonvulsant drugs. Supplementing with 400 mcg of folic acid is sufficient to reduce the risk for women who have no history of neural tube defects, however only 800 mcg or 5 mg tablets are currently available as registered medicines in New Zealand. Mandatory folic acid fortification of bread next year will ensure that all women who become pregnant � planned or unplanned � will receive some preconceptional folic acid.

Sub-optimal iron stores are difficult to replenish once pregnant

A substantial amount of iron is required during pregnancy to meet foetal and maternal needs. About 40% of women aged 15�44 years in New Zealand have an inadequate intake of iron. Adequate pre-pregnancy iron stores may play a role in reducing risk for iron deficiency and anaemia during pregnancy. Sub-optimal iron stores are difficult to replenish once pregnant.

Healthy pre-conception bodyweight improves outcomes

Being underweight or overweight prior to conception can affect birth outcome. Evidence from observational studies suggests that low pre-pregnancy body mass index (BMI, <20 kg/m²) is associated with reduced infant birth weight, and increased incidence of preterm delivery.³ Obese women have an elevated risk for pre-eclampsia, gestational diabetes, neural tube defects and stillbirth, as well as giving birth to a large for gestational age infant.^3,4 More than one quarter of all New Zealand women are obese.⁴

Weight gain during pregnancy influences infant birth weight and health

The U.S. Institute of Medicine recommendations for appropriate weight gain during pregnancy (Table 1) are based on pre-pregnancy BMI and uphold a slightly different range of weight gain for each BMI category. Weight gains within these guidelines are associated with optimal birth weight (between 3000 g and 4000 g) and best labour and delivery outcomes. Women who gain more weight in pregnancy than recommended have a significantly increased risk of having an infant weighing greater than 4000 g.⁵ High birthweight infants tend to be taller and heavier children with increased risk of obesity and metabolic problems in later life.⁶ Excessive prenatal weight gain also places the mother at risk for long-term obesity post-delivery.⁷

Table 1: Current recommendations for weight gain during pregnancy⁶

There are currently no data available to indicate how much weight New Zealand women are gaining during pregnancy. Survey work conducted in the United States and Europe indicates that only a small proportion of women gain within the recommended ranges with excessive weight gain being more prevalent than inadequate weight gain.⁵ Reports indicate that pregnancy weight gain is influenced by recommendations of health care providers so it is important this advice is accurate. Many women receive no prenatal weight gain advice.^8,9

A healthy diet meets most nutrient requirements during pregnancy

Many questions remain unanswered regarding how the mother�s nutritional status influences pregnancy outcome. Consequences of deficient or excessive nutrient intakes are difficult to determine, and assessment of vitamin and mineral status during pregnancy is not easy due to a lack of pregnancy-specific laboratory values. Based on available evidence, a healthy and varied diet can provide adequate energy and meet the mother�s requirements for most nutrients. Selected vitamin and minerals that are likely to be limited in the diets of pregnant women are briefly highlighted.

Folate requirements are high during pregnancy

In addition to reducing neural tube defects, lack of folate during pregnancy is associated with increased risk of preterm delivery, low birth weight and poor foetal growth. The recommended intake of dietary folate is 600 mcg per day. Survey data of pregnant women in New Zealand indicate that dietary intakes of folate are well below recommended levels.⁴

400 mcg folic acid or 600 mcg dietary folate?

The 400 mcg recommendation to reduce neural tube defects is based on folic acid (synthetic form of folate) only. The 600 mcg recommended during pregnancy is in the units of Dietary Folate Equivalents (DFE) (food folate = 1 mcg DFE and folic acid = 1.7 mcg DFE). So essentially the 400 mcg folic acid tablet recommended preconceptional is worth 680 mcg DFEs and pregnant women then meet both recommendations by taking a supplement. Post-closure of the neural tube (after the first trimester) it is recommended that women intake 600 mcg DFEs. It is possible to obtain this all from the diet but this would involve large amounts of foods such as broccoli and spinach. Therefore women are recommended to continue with a folic acid supplement in addition to a folate rich diet for the entire pregnancy. This recommendation stands regardless of fortification of the food supply.

Iron requirements increase throughout pregnancy

Additional iron requirements during pregnancy increase substantially from the first trimester to the third trimester. A recommended dietary intake of 27 mg per day for the entire duration of pregnancy builds iron stores in early pregnancy for the third trimester.

Although women should be encouraged to consume plenty of iron rich foods during pregnancy, obtaining the recommended intake from diet alone is difficult. Survey data of pregnant women in New Zealand indicate mean iron intakes between 11�14 mg per day.⁴ The highest prevalence of low iron stores, iron deficiency and iron-deficiency anaemia is among New Zealand Māori women, particularly aged 15�24 years.⁴ Maternal anaemia is associated with infant mortality and premature delivery.

Post-delivery, a woman who has been iron deficient during pregnancy should have further follow-up as postpartum anaemia is associated with emotional instability, depression and stress.¹⁰

For those who consume no or small amounts of animal source food, or when low iron stores are suspected, a low-dose iron supplement (30 mg ferrous iron per day) taken at bedtime or between meals is advised. When iron deficiency with or without anaemia is diagnosed, larger doses of iron supplements (~100 mg ferrous iron per day) may be advised to improve iron status as early in pregnancy as possible.⁶ Although there is currently insufficient evidence to recommend for (or against) routine iron supplementation of all pregnant women, the U.S. Institute of Medicine, recognises that many women have suboptimal iron stores and advise daily low-dose iron supplementation (30 mg) to all women in the second and third trimesters.

Iodine requirements increase in pregnancy

Requirements for iodine increase in pregnancy due to a marked change in thyroid function. Despite the upcoming mandatory fortification of bread with iodine in 2009, pregnant women will likely have intakes below the recommended level of 220 mcg per day. Median iodine intakes of New Zealand pregnant women are estimated between 60 to 70 mcg per day.¹¹ Iodine deficiency during pregnancy can negatively affect both maternal and infant thyroid function and cognitive development of the infant.

Despite lack of clinical data on the effect of iodine supplementation on birth outcomes in mild to moderately deficient pregnant women,¹² several health authorities recommend that pregnant women consume 150 mcg per day of potassium iodide to prevent deficiency.^{13, 14} Currently there are no single oral iodine preparations available as registered medicines in New Zealand. Seaweed and kelp tablets should not be used as the iodine content in these products is extremely variable and can be toxic.

Iodine supplements are now funded. For more information, see "Snippets: Iodine supplements Zoledronic acid & Atorvastatin", BPJ 30 (August, 2010).

Low vitamin D levels can affect foetal bone

During pregnancy, the lack of vitamin D may adversely affect foetal bone and accumulation of newborn vitamin D stores.¹⁵ Vitamin D increases intestinal absorption of calcium. Rickets is a clinical marker of poor pre- and postnatal bone health caused by vitamin D deficiency. There have been reports that rickets is re-emerging though its prevalence in New Zealand is unknown.

Dietary sources of vitamin D are limited and the main source is skin synthesis on exposure to sunlight. The most recent national survey indicated a high prevalence of vitamin D insufficiency in New Zealanders.¹⁶ Plasma concentration of 25-hydroxyvitamin D is a marker of vitamin D status. A level below 25 nmol/L indicates risk of vitamin D deficiency. A survey of pregnant women from a general practice population in Wellington reported that 87% of women had 25-hydroxyvitamin D below 50 nmol/L.¹⁷

Many experts agree that the recommended adequate intake for vitamin D of 200 IU per day during pregnancy is grossly underestimated.¹⁸ Studies are currently underway to address the effect of vitamin D supplementation during pregnancy on the nutritional vitamin D status in both mother and foetus.

There is little evidence to support other supplements

For all other vitamin and minerals in pregnancy, there is little evidence to support routine supplementation unless inadequate nutrient intakes are suspected.

Women who are taking multivitamin/multimineral supplements should be cautioned to avoid exceeding intake of 10,000 IU (3,330 RE) of vitamin A (retinol) per day.

Get a pdf of the table here