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Birth weight, placental weight and gestation time in relation to natural selection in Thailand.

Abstract：

:Birth weight, placental weight and gestation time of 26258 single births at Ramathibodi Hospital during 1973-7 were studied in relation to natural selection by fitting quadratic function to natural log of survivors-to-nonsurvivors ratios. The survival criterion was 7 days after delivery. The estimated optimal values of birth weight and placental weight were 0.62 and 0.90 standard deviations, respectively, above the corresponding arithmetic means. Selection on birth weight and placental weight was asymmetrical about the optima, being more intense among the lower than the higher values. On the other hand, selection on gestation time seemed most stabilized with the optimum almost coinciding with the mean. :The relations of birth weight, placental weight, and gestation time to neonatal death were analyzed for 26,258 single births during 1973-77 at Ramathibodi Hospital in Bangkok, Thailand. The survival criterion was surviving beyond the 7th day after delivery. The dead included deaths in utero and sillbirths. The death rate was 9.25/1000. Sex specific rates were 9.96 for males and 8.08 for females. All mothers delivering at the hospital received prenatal care and most or all belonged to upper socioeconomic groups. Gestation time was calculated form expected date of confinement and birth date, but only 19,647 cases reported complete expected dates. The estimations of the optimal values of birth weight, placental weight and gestation time were done by fitting quadratic functions to a natural log of survivors-to-nonsurvivors ratios using the model of Karn and Penrose. The male and female optimal birth weight values were 3389.19 and 3332.02 gm respectively, .58 and .67 standard deviations above the corresponding means. From extrapolation, the curve below 2000 gm approached zero more rapidly than that beyond 4200 gm. The relative fitness curve for placental weight followed virtually the same pattern as that for birth weight. Optimal values in males and females were 722.00 and 710.52 gm, or .91 and .89 standard deviations above the respective means. 5 cases whose placentae weighed more than 1300 gm were essentially a separate category in which the chance of survival was zero. The optimal gestation values were 277.43 days for males and 281.15 for females, almost coinciding with the mean values. Females had higher fitness than males at all values, and the gap between the 2 curves widened at the 2 ends. Selection on birth weight and placental weight was asymmetrical about the optima, being more intense among the lower values. Selection on gestation time was symmetrical about the mean, with the optima almost coinciding with the mean.

journal_name

Ann Hum Genet

journal_title

Annals of human genetics

authors

Promboon S,Mi MP,Chaturachinda K

doi

10.1111/j.1469-1809.1983.tb00980.x

subject

Has Abstract

pub_date

1983-05-01 00:00:00

pages

133-41

issue

eissn

0003-4800

issn

1469-1809

journal_volume

pub_type

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Birth weight, placental weight and gestation time in relation to natural selection in Thailand.