A PROSPECTIVE STUDY OF THE PLACENTAL WEIGHT AND CONTENT OF PROTEIN, RNA AND DNA

Folic acid supplementation, dietary folate intake and risk of small for gestational age in China

OBJECTIVE

To investigate the hypothesis that folic acid supplementation and dietary folate intake before conception and during pregnancy reduce the risk of small for gestational age (SGA) and to examine the joint effect of folic acid supplementation and dietary folate intake on the risk of SGA.

DESIGN

Participants were interviewed by trained study interviewers using a standardized and structured questionnaire. Information on birth outcomes and maternal complications was abstracted from medical records and dietary information was collected via a semi-quantitative FFQ before conception and during pregnancy.

SETTING

A birth cohort data analysis using the 2010-2012 Gansu Provincial Maternity and Child Care Hospital.

PARTICIPANTS

Women (n 8758) and their children enrolled in the study.

RESULTS

Folic acid supplementation was associated with a reduced risk of SGA (OR = 0·72, 95 % CI 0·60, 0·86), with the reduced risk seen mainly for SGA at ≥37 weeks of gestational age (OR = 0·70, 95 % CI 0·58, 0·85) and nulliparous SGA (OR = 0·67, 95 % CI 0·54, 0·84). There was no significant association between dietary folate intake and SGA risk.

CONCLUSIONS

Our study suggested that folic acid supplementation was associated with a reduced risk of SGA and the risk varied by preterm status and parity.

From 13 weeks to term, the trophoblast of human placenta grows by the continuous recruitment of new proliferative units: a study of nuclear number using the disector

A method is presented for obtaining assumption-free estimates of the number of nuclei in the trophoblast of the human placenta and for defining the size of the trophoblast proliferative unit (TPU). The method relies on the disector, a stereological device for counting arbitrary particles in 3-dimensional space using pairs of parallel sections separated by a known distance. It is applied to investigate factors which contribute to trophoblast growth from 13 weeks of gestation to term. Physical disectors were sampled systematically using adjacent 4-4.6 microns thick paraffin sections. Nuclei in the trophoblast (syncytial and cellular) were counted if they appeared in an unbiased counting frame on one section but were absent from the adjacent section. Nuclear packing densities were converted to absolute numbers of nuclei by using placental volume as the reference space. At 37-39 weeks, the average placenta contained 6.4 x 10(10) trophoblast nuclei of which 90 per cent were located within the syncytium and the remainder in the cytotrophoblast. From a knowledge of total trophoblast volume, it was found that each nucleus is associated with 970 microns3 of trophoblast and each cytotrophoblast cell with 11,000 microns3. The latter may be regarded as the volume of a TPU. From 13 weeks of gestation to term, there was a ninefold increase in nuclear number but the trophoblast volumes associated with nuclei, including the size of the TPU, remained constant. Growth of trophoblast is purely hyperplastic and occurs by recruitment of new TPUs.

Quantitative description of the elaboration and maturation of villi from 10 weeks of gestation to term

Stereological methods have been applied to a cross-sectional sample of human placentae collected at 10-41 weeks of gestation in order to provide a quantitative description of the growth and maturation of villi. Random tissue sections were analysed to derive volumes, surface areas, lengths, diameters and membrane thicknesses for villi and their fetal capillaries. Expansion of the total volume and surface area of villi can be explained by a dramatic linear growth of terminal villi which begins at about the middle of the second trimester. Growth of intermediate villi also occurs but to a more limited extent. Linear growth is accompanied by villous maturation which involves increases in the relative volume of capillaries and in villous capillarization coupled with decreases in villous diameter, capillary diameter and harmonic thickness of the villous membrane. These findings confirm that placental growth and development depend greatly on growth and maturation of terminal villi. They do not confirm sinusoidal dilation of fetal vessels as a generalized phenomenon. They also support the contention that changes in effective diffusion distances across the villous membrane have real adaptive significance.

Continuing growth and development of the third-trimester human placenta

Two hundred and nineteen human placentae of well ascertained gestational age were measured for weight and nuclear number. Contrary to previous reports, analysis of the results showed no faltering in either parameter, however expressed. The placentae from babies exhibiting intrauterine growth retardation were appropriate to the size of the babies. However else the placenta ages it does not do so in respect of the rate of increase in the number of its nuclei.