Nutrition in Pregnancy and Lactation

Second last post for PHYL3003! Hooray!

Understand the effects of maternal under- and over-nutrition on pregnancy outcomes and long-term health of the offspring

Not too many details were provided here, other than that mothers with a high BMI are more likely to give birth to very large babies, which may increase the risk of complications during delivery. Macrosomia is the term given to a birth weight above 4.5kg, and babies with macrosomia are more likely to develop metabolic syndrome later in life. On the other hand, if mothers do not gain enough weight during pregnancy, there is increased risk of low birth weight and pre-term birth.

Risk factors for inadequate fetal nutrition are age (adolescents are more likely to smoke and are more likely to have iron deficiency), multiple births (twins, triplets etc.), nausea and vomiting during pregnancy, short intervals between pregnancies, and so on. It should also be noted, however, that it is generally not necessary to consume excessive amounts of food during pregnancy as pregnancy tends to improve the efficiency of fat and energy storage.

Describe the changes in glucose metabolism in pregnancy and relevance to maternal & foetal health

Pregnancy is considered to be a state of natural insulin resistance, as insulin sensitivity usually decreases by around half over the course of pregnancy. Placenta-derived TNFα increases circulating free fatty acids and alters phosphorylation of the insulin receptor, decreasing GLUT4 expression and mobilisation (and thus decreasing glucose uptake).

If the mother began with normal insulin sensitivity, chances are that she won't be too badly affected by the decrease in insulin sensitivity. However, mothers who initially had suboptimal insulin sensitivity are at risk of developing gestational diabetes mellitus (GDM). Other risk factors for GDM include a high BMI and excessive gestational weight gain (EGWG) in the firs half of pregnancy.

Discuss physiological adaptations in maternal calcium and iron metabolism in pregnancy and lactation

Calcium

Over the course of pregnancy, around 30g of calcium goes towards fetal skeleton mineralisation (around 2-3 mg/day in the first trimester up to around 250-300mg/day in the third trimester). Nevertheless, dietary requirements remain the same throughout pregnancy and lactation. During pregnancy, total calcium decreases, but ionised calcium remains normal. Calcitriol (vitamin D3) and calcitonin tend to increase during pregnancy, but return to normal afterwards. PTH usually stays the same, but it may decrease if calcium levels are insufficient. In general, calcium requirements are met during pregnancy due to an increased absorption of calcium (due to increased calcitriol), whereas during lactation, the main method of increasing calcium is increased bone resorption.

Iron

Requirements for iron increase significantly during the second and third trimesters, but drop back to normal right after birth. Iron deficiency anaemia is relatively common, and risk factors include being vegetarian or vegan, heavy periods before pregnancy, obesity, and excessive gestational weight gain. Since half of the offspring's iron needs are supplied during gestation, and insufficient iron impairs neurodevelopment, it is important that enough iron is absorbed.

Iron uptake changes during pregnancy due to regulation of hepcidin (discussed here). After around 20 weeks, hepcidin transcription decreases, increasing iron absorption. Hepcidin returns to normal after giving birth. Inflammatory conditions such as preeclampsia, malaria and obesity may increase hepcidin, decreasing iron absorption.

Identify fortification and supplementation strategies to achieve adequate nutrition in pregnancy

Two of the main nutrients that are routinely supplemented during pregnancy are iodine and folate. Insufficient iodine can cause cretinism, so to prevent this many foods are fortified with iodine, and supplementation of 150μg/day is recommended from pre-pregnancy through to lactation. Folate, which is important for neural tube formation, is also routinely supplemented. Usually at least 400μg/day is given for at least one month prior to conception, as well as the first twelve weeks of pregnancy. Patients with an increased risk of neural tube defects and/or folate deficiency may be given more folate. Just like with iodine, many foods are fortified with folate.