How does weight loss affect pregnancy?

I am 18 weeks pregnant and my doctor is concerned about my recent weight loss. How does weight loss affect pregnancy?


Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

In evaluating the health of a mother and baby during antepartal care, we look for patterns. Some patterns of maternal weight gain are more closely related to fetal development and well-being than others.

When a mother gains consistently (three to five pounds in first trimester, 10 to 14 pounds in the second and third) we more reliably see favorable outcomes for mother and baby.

Weight loss can represent fetal growth at the expense of the mother, and, of course, eventually the fetus is compromised as well. Weight loss or gain is only a rough estimate of maternal nutrition stores and intake, but the only objective one we have during an average prenatal care visit. Subjective questioning must always follow some deviation from the expected. For example, the care provider might ask questions about recent illness, nausea and vomiting, exercise, dehydration, rest/sleep patterns, work and stress history, and do a diet recall.

If the care provider conveys that weight loss is only one indicator of pregnancy health, the client is more likely to concentrate on getting essential nutrients rather than filling up on junk food just to see weight gain. If you gain five pounds by the next visit, this does not mean that you have necessarily been eating a good diet. Neither does weight loss translate to a poor diet.

If you honestly believe that your nutrient intake has been adequate, I would not worry. Occasionally, we see weights stabilize or drop after a month of particularly rapid weight gain. Fluctuations are normal; weight gain does not follow a smooth curve.

Some researchers believe that if a mother is not gaining, she is actually losing due to the increasing weights of the components of the pregnancy. If that is true, then she is metabolizing fat, which may cause ketones to be liberated in her blood. Some feel that these may be toxic to developing brains. You can roughly measure ketones in the urine by a dipstick. If the mother is losing weight or experiencing nausea and vomiting, ketones should be checked.

Intrauterine growth retardation is the end result of poor maternal nutrition. If the insult occurs early and is continued, the fetal brain may be compromised and the baby can be born with a symmetrically small head and body. If the deficit occurs later, the brain may be spared and the baby may be born with a smaller-than-average body but normal head and brain development.

This is undoubtedly more than you wanted to know, but in short, if this is not a pattern, I would not be concerned. You may want to monitor your own weight at home each week and be sure that the scale is calibrated correctly and you are wearing approximately the same clothes. Shoes can weigh one or two pounds, so it is best to weigh without shoes at the office or wear the same ones each time. If this continues, you may want to seek the help of a nutritionist.

I hope this helps. Best of luck.

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