In the contemporary Western world where extremes are the norm rather than the exception, it is important to consider what the consequences are. More and more people are underweight. What is the consequence of such extreme weight for our posterity? How does the mother’s weight during pregnancy affect the child? And does this have lifelong consequences for the child? This article will address the question of how being underweight affects the unborn child.
What is the influence of maternal underweight on the unborn child?
One of the influences of being underweight on women is that they are less likely to become pregnant, but when a woman does become pregnant, her low weight brings many complications. Below we discuss why underweight women have reduced fertility and what influence the mother’s underweight has on the development of the fetus during pregnancy.
Reduced fertility
It is often very difficult for underweight women to get pregnant. Many underweight women are often not or less fertile because at a low body weight the hypothalamus is unable to release GnRH in pulsating waves. This GnRH is responsible for releasing FSH and LH, FSH stimulates the growth of follicles in the ovaries and LH is responsible for bursting the largest follicle (Silverthorn, 2013). If a woman is extremely underweight, ovulation and therefore fertilization are not possible.
Increased risk of miscarriages
In addition to the fact that underweight women have reduced fertility, there is also a much greater risk of miscarriage (a birth before 16 weeks of pregnancy). Women with a low BMI have 1.7 times the risk of miscarriage compared to women with a healthy weight (Veleva et al., 2007). The higher rates of miscarriage in people with a low BMI can be explained by the action of leptin, a hormone that is predominantly produced in adipose tissue (Mitchell et al., 2005). Plasma leptin levels correlate with BMI and body fat percentage (Andrico et al., 2002). Leptin and its receptors are expressed in the secretory endomentrium, where they regulate the growth of the uterine wall (Bouloumie et al., 1998) and the implantation of the embryo (Cervero et al., 2004). Low plasma levels of leptin are associated with early and recurrent miscarriage (Lage et al., 1999) and may explain why underweight women have an increased risk of miscarriage.
Greater chance of newborns being underweight
If a miscarriage does not occur, it is still not always certain that the baby will turn out well. Being underweight before pregnancy is a risk factor for reduced fetal growth (Doherty et al. 2006). In women with a low BMI before pregnancy, low birth weight is twice as common as in women with a healthy weight. (Jeric et al., 2013). We speak of a low birth weight when a baby has a weight that is too low for the duration of the pregnancy. The term SGA is used for this, this abbreviation stands for Small for Gestational Age.
Effects of maternal weight
Women who are underweight before pregnancy have significantly higher incidences of spontaneous preterm birth and SGA than women who are normal weight before pregnancy. We speak of a premature birth when the child is born after a pregnancy shorter than 37 weeks.
In addition, it is important for pregnant mothers to gain enough weight during pregnancy. It appears that both underweight women and women with normal pre-pregnancy weight are more likely to have spontaneous preterm birth if they gain less weight per week than recommended by the IOM (Institute of Medicine) guidelines. Cases of SGA only occur significantly more often in women who were underweight before pregnancy and who gained too little weight per week (Fujiwara et al., 2014). It is not yet entirely clear what causes premature birth in underweight women and women who gain too little weight during pregnancy. It appears that placental dysfunction due to long nutritional deficiencies and gestational anemia causes additional stress hormones to be released. These hormones, such as norepinephrine and cortisol, increase the concentration of corticotropin-releasing hormone and promote the production of prostaglandins, which induce labor (Fujiwara et al., 2014). The lack of important nutrients for the immune system, such as zinc and iron, can also cause infections and inflammation to occur more quickly, increasing the risk of premature birth. (Fujiwara et al., 2014)
Required weight gain
It is important that the mother gains weight during pregnancy for the development of the baby. Usually the mother’s weight gain in the first trimester is minimal, only at the end of this trimester does the weight begin to accumulate. In the second and third trimesters, weight gain becomes linear (Pitkin & Spellacy, 1978). When the mother gains 1 kg in the first semester, this means a weight gain of 18 grams at birth weight, gaining 1 kg in the second semester results in 32.8 grams. grams of extra birth weight and in the third semester for 17 grams. This shows that when a mother has difficulty gaining weight in the second semester, this has the most impact.
To calculate what an underweight pregnant woman needs to gain per week, the following formula can be used:
kg to gain per week = kg underweight / weeks until delivery.
There are various results from studies into how many kcals need to be consumed for a baby. certain weight gain. For example, researchers claim that for an increase of 0.45 kg per week, 750 kcal to 800 kcal per day must be consumed (Calloway & Carpenter, 1981), but another study suggests that for the same weight gain an intake of 500 kcal and 20 grams proteins (Leonard. 1984).
Consequences of missing nutrients
It is not only weight that plays an important role in pregnancy. It is also important for pregnant women to pay attention to nutrients. Iron and glucose, among other things, are very important for pregnant women.
Many underweight women (particularly women with anorexia) have a deficiency of iron in their blood. The biggest cause of iron deficiency is low consumption of fish, meat or poultry (Black et al. 2008). To combat iron deficiency during pregnancy, it is recommended to increase iron intake from 9 mg to 21 mg per day (Institute of Medicine, 2001). The iron deficiency can lead to anemia. Anemia during pregnancy can then lead to premature children and children with a low birth weight. Having moderate anemia can lead to a twice as high risk of maternal death. The mechanisms associated with increased mortality in pregnant women with anemia are not well understood. Heart failure, bleeding and infections are identified as possible causes (institute of medicine, 2001)
Effects of fasting during pregnancy
When women fast during pregnancy (due to an eating disorder or, for example, a lack of food), adjustments occur in the woman’s metabolism. The secretion of the steroid hormone hPL (human placental lactogen) from the placenta changes. This hormone mobilizes maternal fatty acids and thus saves glucose for the fetus and placenta. In fasting pregnant women, the release of hPL is increased due to, among other things, low blood sugar levels (Kitzmiller, 1980). The increase in hPL can be seen in the blood by a rapid increase in fatty acid and ketone concentrations (Schreiner et al., 1980). During pregnancy, the glucose concentration in the blood changes. In women who eat normally, this is a small change, but it does occur and the concentration of glucose gradually decreases during pregnancy. Various metabolic reactions that occur during a period of fasting are extra intense in pregnant women. The effects are stronger in both time and quantity. This general appearance is called accelerated starvation. This is also clearly reflected when you look at glucose. The gradual small change that occurs in healthy women is rapid and large in underweight women. Several studies have been done in animals (Steel & Leng, 1973) supporting the hypothesis that the increase in glucose turnover during pregnancy is a direct result of the growing mass of the fetus in the mother’s abdomen. This means that the more glucose the woman has in her body, the better the fetus can grow. This once again shows how important it is for a pregnant woman to get enough nutrients for the development of the child.
Conclusion
Women who start a pregnancy underweight take a considerable risk. A large number of things can go wrong leading to premature birth and also stunted growth for the unborn children. In addition, it is important for all pregnant women to gain enough weight during pregnancy.
