There are many symptoms and complications associated with Nausea and Vomiting of Pregnancy (NVP); women may eat much less or much more (to prevent nausea), be less hydrated, eat less nutritious foods, and may even be deficient in one or more vitamins or minerals. Women are therefore often worried about NVP affecting their baby.
However, NVP is often cited as a positive, healthy sign of a progressing pregnancy, in that the causes or contributing factors leading to NVP are continuing (most likely a result of hormones).
There is less data regarding risk of miscarriage when NVP fades or suddenly stops, which can happen, but often results in a normal pregnancy. This is difficult to assess overall, however, because at some point, NVP does go away in almost all women who go on to have healthy pregnancies. Further, some women do not experience any NVP at all, and also have healthy, full term pregnancies.
Any currently negative-associated affects of NVP on the embryo/fetus – even weak associations – appear to be highly dependent on the longevity and severity of symptoms as well as the presence of complications in the mother.
NVP has been strongly associated with a reduced risk of miscarriage, to include nausea without vomiting.
One study indicated that pregnancy loss (prior to 20 weeks) among those experiencing NVP symptoms ranged from 0% to 11%, while pregnancy loss among women without NVP ranged from 7% to 35%. The pregnancy loss rate among those who also vomit may be even lower, estimated around 1% to 5% (as opposed to nausea without vomiting).
Further, it is possible for NVP to stop suddenly. One study noted that nearly 40% of the women studied had symptoms that stopped suddenly, rather than gradually tapering over a period of weeks (note: the pregnancy outcomes in these women were not indicated).
Therefore, it does not appear the absence or sudden absence of NVP indicates a pregnancy is in danger. However, the pregnancy outcomes in women with NVP that “suddenly” stops has not been fully followed or studied, and women begin to feel better at different times in the first and second trimesters. Additionally, NVP does not eliminate miscarriage risk.
The mechanism by NVP can protect a fetus is not known, but hypotheses include the possibility of a protective factor against ingestion of potential toxins.
The prevention hypothesis, a popular theory first presented more than 30 years ago, indicates NVP is protective mechanism and evolutionary trait; nausea and/or vomiting as well as its associated aversions helps pregnant women protect their embryo through the avoidance of foods that may contain chemicals/toxins (read more).
For this theory to be more accurate, it would need to be determined that toxins cause miscarriage. Meaning, that women with no NVP are ingesting toxins or chemicals that eventually lead to miscarriage. However, it is also possible this is an evolutionary trait that no longer applies to more modern times (due to food safety, etc.), and remains simply a trait in which women still feel the effects of, but is technically "no longer necessary".
Nutrition and Growth
In general, miscarriage due to nutrition status is rare, and sole deficiency of one nutrient or moderate deficiencies in several does not appear to increase risks for miscarriage – even in extreme cases such as Hyperemesis Gravidarum (HG).
Fortunately, during embryonic development, the yolk sac has been suggested to play an important role in independent nutrient delivery (regardless of the mother's status), and may be the major, and possible the only source of certain nutrients for the embryo in early pregnancy.
Further, it has been reported that severe vomiting that lasts longer during pregnancy (past 20 weeks) is more likely to cause effects such as decreased birth weight, than if vomiting ceases earlier in pregnancy.
Overall, evidence for these types of birth outcomes related to NVP and HG remain inconsistent. While some studies have reported a reduction in fetal growth in women who lost a lot of weight early in pregnancy, other studies have found a reduced risk of both preterm delivery and growth restriction in those with NVP.
Overall, NVP does not appear to increase the risk for birth defects.
In a study of more than 16,000 women, no difference was found in birth defects between those with or without NVP, and a separate study found a lower risk of congenital heart defects in infants born to women with early onset NVP.
Additionally, an increased risk for NTDs conflicts with evidence that the fetus is relatively well-protected from malnutrition early in pregnancy. Further, the neural tube (eventual brain and spinal cord) closes by 6 weeks of pregnancy, and most women will not experience NVP that could affect their nutrition until later in the first trimester.
However, it is possible that severe symptoms could still affect the fetal brain. A study published in September 2020 indicated severe NVP was strongly associated with psychiatric and cognitive problems in children, due to alterations in brain structure. However, how severe symptoms could lead to this association was not understood, but maternal stress was assessed to be plausible.
Women with HG tend to have more extreme symptoms and malnutrition for longer periods, but, overall, research regarding physical or developmental adverse effects on a baby born to a woman with HG remain inconsistent.
While studies have indicated a higher risk of colic, irritability, growth restriction, low birth weight, and various birth defects, others have found no association and indicate that women with HG should be reassured their infant will likely be born healthy.
If women are suffering from severe NVP but are still able to remain even somewhat nourished and hydrated, they should not be concerned about their baby's health. Current research indicates that even in extreme cases, most babies will be born without problems.
However, because research remains ongoing, and certain outcomes have not been thoroughly studied, women who lose too much weight, or experience prolonged periods without adequately eating or drinking, should call their for a full evaluation.
In addition, women should call their health care provider (HCP) immediately if they:
Experience severe nausea, vomiting, abdominal pain, and/or weight loss
See blood in vomit, which could be red or black
Cannot keep fluids down; experience symptoms of dehydration
Pass only a small amount of urine or urine is a dark color
Have a fever
Have a rapid heart rate
Experience dizziness, faintness, tiredness, or confusion
Partners and family members can remind women they are going through NVP for a reason. NVP is a healthy sign the baby is developing well, and will likely suffer no ill effects from how she is feeling, or any prenatal vitamins she may have forgotten to take. However, the avoidance of major nutrient deficiencies is important, and women with severe symptoms should see their HCP as early as possible who can help her manage her nutrition – and symptoms – effectively.
Nausea and Vomiting of Pregnancy (Gastroenterol Clin North Am. 2011 Jun)
Nausea and Vomiting of Pregnancy-What’s New? (Auton Neurosci. 2017 Jan)
Morning Sickness: Nausea and Vomiting of Pregnancy (American College of Obstetricians and Gynecologists)
Nausea and Vomiting of Pregnancy: Committee Opinion 189; January 2018 (American College of Obstetricians and Gynecologists)
Problems of the Digestive System (American College of Obstetricians and Gynecologists)