Table 1.
Maternal characteristics at enrollment by number of fetuses and pregnancy characteristics, NICHD Fetal Growth Studies: Twin Gestations (N=171).
| Maternal Characteristic | n (%) |
|---|---|
| Race/ethnicity | |
| White/non-Hispanic | 93 (54.5) |
| Black/non-Hispanic | 36 (21.1) |
| Hispanic | 33 (19.3) |
| Asian | 8 (4.7%) |
| Multiracial | 1 (0.6%) |
| Age, years – Mean (±SD) | 31.6 (±6.1) |
| Gravidity | |
| 1 | 51 (29.8) |
| 2 | 59 (34.5) |
| 3+ | 32 (18.7) |
| Parity | |
| 0 | 96 (56.1) |
| 1 | 54 (31.6) |
| 2+ | 21 (12.3) |
| Maternal height, measured (cm) – Mean (±SD) | 165.1 (±6.4) |
| Prepregnancy weight, self-reported (kg) - Mean (±SD) | 75.4 (±20.2) |
| Prepregnancy BMI (kg/m2) | |
| < 25.0 | 67 (39.2) |
| 25.0 – 29.9 | 39 (22.8) |
| 30.0+ | 65 (38.0) |
| Mean (±SD) | 28.6 (±7.0) |
| Marital status | |
| Never married | 32 (18.7) |
| Married/living as married | 135 (78.9) |
| Divorced/Separated/Widowed | 4 (2.3) |
| Education | |
| < High school | 12 (7.0) |
| High school | 22 (12.9) |
| Some college | 29 (17.0) |
| College undergraduate | 70 (40.9) |
| Postgraduate college | 38 (22.2) |
| Family income: | |
| ≤$29,999 | 35 (20.5) |
| $30,000–49,999 | 9 (5.3) |
| $50,000–$74,999 | 14 (8.2) |
| $75,000–$99,999 | 18 (10.5) |
| ≥$100,000 | 79 (46.2) |
| Health insurance: | |
| Private/managed care | 117 (68.4) |
| Medicaid; other | 40 (23.4) |
| Self-pay | 3 (1.8) |
| Current student: | |
| Yes | 14 (8.2) |
| No | 157 (91.8) |
| Number of current paid jobs: | |
| 0 | 37 (21.6) |
| 1 | 126 (73.7) |
| ≥2 | 8 (4.7) |
| Smoked cigarettes in the past 6 months | |
| Yes | 26 (15.2) |
| No | 144 (84.2) |
| Missing | 1 (0.6) |
| Frequency of alcoholic beverages in the past week | |
| 5 or more times | 0 |
| 2–4 times | 1 (0.6) |
| Once | 3 (1.8) |
| Not at all | 167 (97.7) |
| Conception by ovulation stimulation drugs or assisted reproductive technology | |
| In vitro fertilization (IVF) | 46 (26.9) |
| Intrauterine insemination (IUI) | 10 (5.8) |
| Medications without IVF or IUI | 11 (6.4) |
| Donor eggs, donor embryos | 13 (7.6) |
| None of the above | 91 (53.2) |
| Medical Diseases | |
| Hypothyroid | 11 (6.4) |
| Hyperthyroid | 0 |
| Pregestational Diabetes | 3 (1.8) |
| Asthma | 15 (8.8) |
| Chronic hypertension | 10 (5.8) |
| Cardiovascular disease | 1 (0.6) |
| Anemia | 17 (9.9) |
| Kidney disease | 0 |
| Autoimmune disease | 6 (3.5) |
| Epilepsy | 1 (0.6) |
| HIV | 1 (0.6) |
| Eating disorder | 3 (1.8) |
| Mood disorder, psychiatric disorder, anxiety or depression | 17 (9.9) |
| Other medical condition | 27 (15.8) |
| Pregnancy Outcome (twin/twin) | |
| Live birth ≥ 20 weeks/live birth ≥ 20 weeks | 152 (88.9) |
| Live birth ≥ 20 weeks/fetal death ≥ 20 weeks | 3 (1.8) |
| Fetal death ≥ 20 weeks/fetal death ≥ 20 Weeks | 3 (1.8) |
| Fetal death ≥ 20 weeks/miscarriage < 20 Weeks | 1 (0.6) |
| Fetal death unknown GA/fetal death unknown GA | 1 (0.6) |
| Miscarriage <20 weeks/miscarriage <20 Weeks | 1 (0.6) |
| Miscarriage/unknown outcome | 1 (0.6) |
| Voluntary termination or fetal reduction/same | 1 (0.6) |
| Voluntary termination or fetal reduction/Unknown outcome | 3 (1.8) |
| Unknown outcome/unknown outcome | 5 (2.9) |
| Neonatal sex | |
| Singleton Male or Twins Male/Male | 45 (26.3) |
| Singleton Female or Twins Female/Female | 41 (24.0) |
| Twins Male/Female | 70 (40.9) |
| Twins Male/Unknowna | 1 (0.6) |
| Twins Unknown b | 14 (8.2) |
| Zygosity (same sex twins only) | |
| Monozygotic | 15 (8.8) |
| Dizygoticc | 133 (77.8) |
| Missing with same sex twinsd | 8 (4.7) |
| Missing neonatal sex and zygosity | 15 (8.8) |
Abbreviations: GA, gestational age; SD, standard deviation
a
Twin A was an antepartum fetal death, and twin B was a miscarriage < 20 weeks.
b
Included 11 women who deactivated from the study, 2 women with live birth of both twins but neonatal sex not recorded, and 1 pregnancy with no chart review performed so neonatal outcome and sex unknown.
c
Includes 70 male and female twin pairs and 63 same sex pairs that resulted as dizogotic by zygosity testing.
d
Zygosity testing not performed due to miscarriage/demise (n=4), participant refusal (n=3), or failed DNA extraction due to inadequate sample (n=1)