Table 2. Maternal KIR2DS1 significantly increases birth weight when the fetus has more HLA-C2 epitopes than the mother (Table 2A) and when a single fetal C2 is paternally but not maternally derived (Table 2B).
| A. Maternal KIR2DS1 significantly increases birth weight when the fetus has more HLA-C2 epitopes than the mother. | ||||||
|---|---|---|---|---|---|---|
| Categorical analysis* | ||||||
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| Subjects | Maternal KIR2DS1 genotype | Median birth weight | High birth weight | Effect of KIR2DS1 on birth weight | ||
| (6 - 89th centile) | (>89th centile) | OR | 95% CI | p value | ||
| Less C2 in fetus than mother (n=280) |
Positive Negative |
n = 76 (35.3%) n = 139 (64.7%) |
n = 25 (38.5%) n = 40 (61.5%) |
1.25 | 0.70 2.26 | 0.45 |
| Equal C2 in fetus and mother (n=725) |
Positive Negative |
n = 215(39.6%) n = 328 (60.4%) |
n = 75 (41.2%) n = 107 (58.8%) |
1.10 | 0.78 1.55 | 0.59 |
| More C2 in fetus than mother (n=304) |
Positive Negative |
n = 95 (40.8%) n = 138 (59.2%) |
n = 47 (66.2%) n = 24 (33.8%) |
2.93 | 1.66 5.18 | 0.0002 |
| Continuous analysis** | ||||
|---|---|---|---|---|
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| Subjects | Effect of KIR2DS1 on birth weight (g) | |||
| n | Mean increase (g) | SE | p | |
| Less C2 in fetus than mother | 280 | 55 | 70 | 0.43 |
| Equal C2 in fetus and mother | 725 | 43 | 46 | 0.35 |
| More C2 in fetus than mother | 304 | 245 | 66 | 0.0002 |
| B. Maternal KIR2DS1 significantly increases birth weight when a single fetal C2 is paternally but not maternally derived. | ||||||
|---|---|---|---|---|---|---|
| Categorical analysis* | ||||||
|
| ||||||
| Subjects | Maternal KIR2DS1 genotype | Median birth weight | High birth weight | Effect of KIR2DS1 on birth weight | ||
| (6 - 89th centile) | (≥90th centile) | OR | 95% CI | p value | ||
| Single fetal C2 paternal (n=204) |
Positive Negative |
n = 61 (38.9%) n = 96 (61.1%) |
n = 29 (61.7%) n = 18 (38.3%) |
2.65 | 1.34 5.26 | 0.005 |
| Single fetal C2 maternal (n=102) |
Positive Negative |
n = 28 (37.3%) n = 47 (62.7%) |
n = 9 (33.3%) n = 18 (66.7%) |
0.81 | 0.31 2.11 | 0.67 |
| Continuous analysis** | ||||
|---|---|---|---|---|
|
| ||||
| Subjects | Effect of KIR2DS1 on birth weight (g) | |||
| n | Mean increase (g) | SE | p | |
| Single fetal C2 paternal | 204 | 196 | 81 | 0.016 |
| Single fetal C2 maternal | 102 | 42 | 130 | 0.75 |
Presence versus absence of KIR2DS1 was tested for effect on birth weight as a categorical variable by logistic regression. UK and Norway cohorts were combined and then analysed in groups defined by combinations of maternal and fetal HLA-C type (Table 3). Cohort and sex of the baby were included as covariates. n = number of pregnancies, OR = odds ratio and CI = confidence interval.
Presence versus absence of maternal KIR2DS1 was tested for an effect on birth weight as a continuous variable in linear regression models of subsets of pregnancies >5th birth weight centile defined by maternal/fetal HLA-C genotype (Table 3). Cohort and sex of the baby were included as covariates. n = number of pregnancies analysed, mean = the average increase in birth weight (in grams) conferred by presence of KIR2DS1 and SE = standard error.