Table 1.
Typology of research concerned with selection in utero, with key examples from the literature.
|
Inference to which gestations |
||||
|---|---|---|---|---|
| Population | Males | Other frail subgroup | ||
|
Endemic Selection |
Based on observed losses | 1 | 3 | 5 |
| Wilcox et al., 1988: In prospective study of 221 women, 31% of pregnancies end before a live birth. | Macdorman et al., 2007: Using US Vital Statistics, they report a 10% excess in male fetal deaths (vs. females). | Hardy et al., 2016: 60% of 8,319 tissue samples from spontaneous abortions show a chromosomal anomaly; percent elevated for mothers >35 years. | ||
| Avalos et al., 2012: Meta-analysis which estimates spontaneous pregnancy loss of 11-22% between 5th and 20th week of gestation. | Byrne & Warburton, 1987: In a clinical series of 683 cases, sex ratio (M:F) of chromosomally normal pregnancy losses is 1.30. | Nybo Anderson et al., 2000: In prospective study of 1.2 million pregnancies, risk of spontaneous loss increases rapidly with maternal age >35 years. | ||
| Cousens et al., 2011: Using official fetal death registration data, they report 2% fetal loss in 3rd trimester. | Orzack et al., 2015: Using 139,00 embryos from in vitro fertilization clinics, Authors estimate that, at conception, 50.2% of embryos are male. | Harlap & Shiono, 1980: Self-reported maternal alcohol use in 2nd trimester varies positively with pregnancy loss. | ||
| Flenady et al., 2011: Risk of loss >20th week elevated among mothers with lower education level. | ||||
|
Inferred from live births or fertility histories |
2 | 4 | 6 | |
| Casterline, 1989: Spontaneous pregnancy loss estimates from self-report in World Fertility Survey range from 3.7 to 14.9%. | Tyson, Parikh, Langer, Green, & Higgins, 2008: Males more common (54%) among 4,000 periviable live births delivered 22 - 25 weeks. | Leridon, 1977: Strong relation between advanced maternal age and pregnancy loss. | ||
| Zeitlin et al., 2002: In pooled analysis of 24 studies, males show a 12% increased odds of delivery <37 weeks (vs. females). | Gage, Fang, O’Neill, & DiRienzo, 2010: Based on US vital statistics, excess fetal loss among non-Hispanic blacks could account for the live birth health advantage of light, frail infants. | |||
| Platt et al., 2004: Health advantages at birth of some allegedly “high-risk” pregnancies may arise due to selection against frail fetuses late in gestation. | ||||
| Epidemic Selection | Based on observed losses | 7 | 9 | 11 |
| Haberg et al., 2013: Mother’s influenza during pregnancy varies positively with pregnancy loss >12th week. | Catalano et al., 2005: In California, the risk of male relative to female losses >20th week rises one month after rises in the unemployment rate. | |||
| Strand et al., 2012: Increased risk of fetal death late in pregnancy during high temperatures. | Bruckner et al., 2010: The terrorist attacks of September 11, 2001 correspond with a nationwide rise in male (relative to female) fetal loss >20th week. | |||
| Faiz et al., 2012: Modest increase in pregnancy loss >20 weeks following exposure to specific air pollutants. | ||||
| Hogue et al., 2013: Positive relation between self-reported significant life events and loss >20 weeks. | ||||
| Inferred from live births or fertility histories | 8 | 10 | 12 | |
| Schneider, 2017: Using 19th century data, liveborn infants in “high” stillbirth rate years show a heavier than expected birthweight distribution. | Catalano, Bruckner, Marks, & Eskenazi, 2006: Sex ratio in New York City fell months after the terrorist attacks of September 11, 2001. | |||
| Cai & Feng, 2005: Increased risk of self-reported pregnancy loss during the Great Leap Forward Famine and Cultural Revolution in China. | Torche & Kleinhaus, 2011: Decline in sex ratio among those exposed to Tarapaca earthquake at three months’ gestation. | Auger et al., 2017: Among > 700,000 pregnancies in Quebec, extreme ambient heat exposure during 1st trimester varies positively with risk of live-born atrial septal (heart) defect. | ||
| Almond & Mazumder, 2011: Decline in male births among Arab mothers exposed to Ramadan fast in the 1st month gestation. | ||||
| Bruckner et al., 2015: Males born to low sex ratio cohorts show better health than do males in other cohorts. | ||||