Why morning sickness is linked to a reduced chance of miscarriage

Yesterday, a new study was published in JAMA Internal Medicine in which they found a clear link between a woman having NVP (i.e., "morning sickness") and a lower chance of miscarriage:

Results A total of 797 women (mean [SD] age, 28.7 [4.6] years) had an hCG-confirmed pregnancy. Of these, 188 pregnancies (23.6%) ended in loss. At gestational week 2, 73 of 409 women (17.8%) reported nausea without vomiting and 11 of 409 women (2.7%), nausea with vomiting. By week 8, the proportions increased to 254 of 443 women (57.3%) and 118 of 443 women (26.6%), respectively. Hazard ratios (HRs) for nausea (0.50; 95% CI, 0.32-0.80) and nausea with vomiting (0.25; 95% CI, 0.12-0.51) were inversely associated with pregnancy loss. The associations of nausea (HR, 0.59; 95% CI, 0.29-1.20) and nausea with vomiting (HR, 0.51; 95% CI, 0.11-2.25) were similar for peri-implantation losses but were not statistically significant. Nausea (HR, 0.44; 95% CI, 0.26-0.74) and nausea with vomiting (HR, 0.20; 95% CI, 0.09-0.44) were associated with a reduced risk for clinical pregnancy loss.Conclusions and Relevance  Among women with 1 or 2 prior pregnancy losses, nausea and vomiting were common very early in pregnancy and were associated with a reduced risk for pregnancy loss. These findings overcome prior analytic and design limitations and represent the most definitive data available to date indicating the protective association of nausea and vomiting in early pregnancy and the risk for pregnancy loss.

http://archinte.jamanetwork.com/article.aspx?articleid=2553283

Why does morning sickness go along with a pregnancy that is less likely to miscarry? I think it is because a lack of hydrogen sulfide, which is necessary to good placental blood vessel development as mentioned in yesterday's post, causes there to be a lower level of toxic sulfite--a hydrogen sulfide product--in the abdomen. An accumulation of sulfite is irritating to mucosal lining in the gastrointestinal tract, thus bringing on nausea and vomiting. Therefore, a pregnancy that isn't developing well is less likely to bring on NVP.

Does that mean that a woman without NVP needs to be frightened that she'll miscarry? The answer to that depends on how good her body is at breaking down sulfite. If she is making enough hydrogen sulfide for a healthy pregnancy but is also breaking down the resulting sulfite quickly, then she will likely have little or no NVP. But if her body is not making enough hydrogen sulfide, that would appear to be a bad portent for the pregnancy's outcome.

For more information on this theory, please see my YouTube video at https://www.youtube.com/watch?v=TaweHPbUPL0.