Table 1. Summary of the study population.
| Characteristic (range) | Never smoked | Smoked early | Smoked throughout |
|---|---|---|---|
| Number of twin pregnancies | 23 | 11 | 12 |
| Mother age at birth | 37 (27–44) | 35 (21–44) | 33 (19–48) |
| Mother BMI | 25 (20–33) | 24 (18–31) | 25 (18–45) |
| Gestational age | 36 (32–38) | 37 (36–38) | 37.2 (34–38) |
| Birth weight (average of 2 twins) kg | 2.60 (1.8–3.2) | 2.71 (2.2–3.4) | 2.61 (2.1–3.7) |
| Birth weight discordance (%) | 9.74 (0.4–27.3) | 11.22 (1.0–27.8) | 9.88 (0.8 – 20.2) |
| Zygosity | 8 MZ, 15 DZ | 4 MZ, 7 DZ | 4 MZ, 8 DZ |
| Sex | 21 M, 25 F | 8 M 14 F | 13 M, 11 F |
| IVF | 6 | 1 | 4 |
| Maternal serum folate at 28 wk (nmol/L) | 33.7 (14.0–64.2) | 32.3 (12.5–46.2) | 29.0 (8.4–42.5) |
| Maternal drinking early pregnancy (drinks / week) | 1.6 (0–10) | 4.5 (0–15) | 1.6 (0–12) |
|
No. cigarettes / day Pre-conception |
0 | 7.0 (1–20) | 13.6 (2–30) |
|
No. cigarettes /day Knew about pregnancy |
0 | 6.2 (1–15) | 13.1 (2–30) |
|
No. cigarettes / day at 24 wk |
0 | 0 | 6.5 (1–15) |
|
No. cigarettes / day at 36 wk |
0 | 0 | 6.3 (1–15) |
| CBMCs | 23 | 11 | 12 |
| Buccal epithelium | 9 | / | 8 |
| Placenta | 8 | 8 | 8 |