shows the characteristics of the mothers, babies and placentas. In comparison with Western populations, the mothers were young, short in stature, and had a high fat mass in relation to body weight. Fifty-one percent were primiparous. The babies had a low mean birthweight and placental weight. Birthweight was correlated with placental weight (r=0.61) but shows that there was a wide variation in placental weight for any given birthweight. For example babies weighing around 3000 g had placentas ranging from 300 to 700 g in weight. Birthweight was also correlated with the length (r=0.40), breadth (r=0.41) and area (r=0.44) of the placental surface. relates the different measurements of maternal body size to birthweight and placental size, shape and efficiency. All four maternal measurements were positively related to the babies’ birthweights, with the strongest effects from maternal head circumference and fat mass.
Characteristics of the mothers, newborns and placentas
Standardised birthweight and placental measurements according to maternal body size
Placental size and shape
The mother’s height was not related to any placental measurement. Larger maternal head circumference, arm muscle area and fat mass were all associated with heavier placental weight; again, the strongest effects were with maternal head circumference and fat mass (). The size and shape of the placental surface were only related to maternal head circumference and maternal fat mass. Larger maternal head circumference predicted a large length-breadth difference, that is a more oval placental surface, while higher maternal fat mass predicted a larger placental surface. We examined the combined effects of maternal fat mass and head circumference on the size of the surface. In a simultaneous regression, increase in fat mass was associated with increasing length (p=0.02), breadth (p=0.009) and area (p=0.007). In contrast, increasing head circumference was associated with reduced breadth (p=0.009), and area (p=0.06) but not length (p=0.45). Maternal age was not associated with birthweight or with any of the placental measurements.
No measure of maternal size was related to the ratio of placental weight to birthweight. Ratios of placental surface size to birthweight fell with increasing maternal head circumference, fat mass and arm muscle area. In a simultaneous regression increasing head circumference and fat mass were both associated with a reduced length to birthweight ratio (p=0.007 and p=0.02) and with a reduced breadth to birthweight ratio (p<0.001 and p=0.05). Increased arm muscle area was associated with a reduced breadth to birthweight ratio ().
shows that, in the sub-sample for whom the mother’s birthweight was available, higher maternal birthweight was related to higher birthweight in the baby. Maternal birthweight was not related to the size of the placental surface but higher birthweight was associated lower ratios of the length and breadth of the surface to birthweight.
Birthweight and placental measurements according to the mother’s birthweight
Sex, parity and maternal age
There were no significant differences between the sexes in any of the associations described. Higher maternal parity was associated with increased birthweight (p=0.02), placental weight (p=0.01), breadth (p=0.01) and area (p=0.05) but not length. Maternal parity was not related to any of the measures of placental efficiency. None of the findings in were changed by adjusting the regression analyses for maternal parity. Maternal age was not related to placental size, shape or efficiency.