The influence of maternal hematocrit on placental development from the first to the second trimesters of pregnancy

Gestation-Specific Changes in the Anatomy and Physiology of Healthy Pregnant Women: An Extended Repository of Model Parameters for Physiologically Based Pharmacokinetic Modeling in Pregnancy

BACKGROUND

In the past years, several repositories for anatomical and physiological parameters required for physiologically based pharmacokinetic modeling in pregnant women have been published. While providing a good basis, some important aspects can be further detailed. For example, they did not account for the variability associated with parameters or were lacking key parameters necessary for developing more detailed mechanistic pregnancy physiologically based pharmacokinetic models, such as the composition of pregnancy-specific tissues.

OBJECTIVES

The aim of this meta-analysis was to provide an updated and extended database of anatomical and physiological parameters in healthy pregnant women that also accounts for changes in the variability of a parameter throughout gestation and for the composition of pregnancy-specific tissues.

METHODS

A systematic literature search was carried out to collect study data on pregnancy-related changes of anatomical and physiological parameters. For each parameter, a set of mathematical functions was fitted to the data and to the standard deviation observed among the data. The best performing functions were selected based on numerical and visual diagnostics as well as based on physiological plausibility.

RESULTS

The literature search yielded 473 studies, 302 of which met the criteria to be further analyzed and compiled in a database. In total, the database encompassed 7729 data. Although the availability of quantitative data for some parameters remained limited, mathematical functions could be generated for many important parameters. Gaps were filled based on qualitative knowledge and based on physiologically plausible assumptions.

CONCLUSION

The presented results facilitate the integration of pregnancy-dependent changes in anatomy and physiology into mechanistic population physiologically based pharmacokinetic models. Such models can ultimately provide a valuable tool to investigate the pharmacokinetics during pregnancy in silico and support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Fetal haematocrit is a determinant of placental size in term pregnancies

Placental size may be influenced by maternal factors, placental function as well as the fetal condition. So far, no studies have examined how the fetal oxygen-carrying capacity or haemoglobin/haematocrit levels would affect placental growth in normal human pregnancies. The aim of this study was to investigate the relationships between placental size and fetal arterial cord blood haemoglobin and haematocrit levels at the time of caesarean delivery. Umbilical arterial cord blood was taken for arterial haemoglobin and haematocrit levels immediately after delivery. The relative placental size (defined by the ratio of placental weight to fetal weight) was inversely correlated with both arterial haemoglobin (r = -0.455, p = 0.001) and haematocrit levels (r = -0.425, p = 0.003) in women who had undergone elective caesarean sections. No significant correlation was found between the relative placental size with other maternal and fetal factors.

First and second-trimester biochemical markers of chromosomal anomalies and their relationship to maternal haemoglobin levels

OBJECTIVE

To evaluate a previous hypothesis that maternal serum biochemical markers used in the assessment of Down syndrome risk are related to maternal haemoglobin concentrations.

METHODS

A series of 1306 second-trimester prenatal screening records were retrieved including information on marker levels (AFP and fbetahCG MoMs), Down's risk, a priori age risk, maternal weight and maternal height. Each individual record was merged with data from haematological investigations on samples collected on the same day. A similar series of 1688 first-trimester screening records were also retrieved including the maker levels for PAPP-A, and fbetahCG MoMs were merged with data from haematological investigations carried out on the same day. The two groups were categorised according to their haemoglobin levels; anaemic (less than 11.0 g/dL in first trimester and 10.5 g/dL in the second trimester), high haemoglobin (greater than 14.0 g/dL and 13.2 g/dL) or normal (between these ranges). An analysis was made of marker levels in the various groups before and after correction for ethnicity and of the screen-positive rate in the various groups. Using a formula based on maternal height and weight, variation of marker levels with plasma volume was assessed.

RESULTS

In the first trimester, 12.6% of the pregnant population was anaemic and 1.6% had elevated haemoglobin levels. In the second trimester this was 12.7 and 3.9%. These figures varied considerably with ethnic origin, with Asian and Afro-Caribbean women being more anaemic than Caucasian women. Haemoglobin levels declined by 7% between the 11- and 21-week period. Maternal plasma volume (as calculated by a widely used maternal height and weight relationship) was not correlated with weight-corrected biochemical marker MoMs in either trimester. A weak but significant correlation of maternal plasma volume and haemoglobin concentration was observed. There was no significant correlation between biochemical marker MoMs and haemoglobin concentration. Although the proportion of pregnancies designated screen positive decreased as haemoglobin levels increased, this was paralleled by a decrease in the maternal age a priori risk.

CONCLUSIONS

There is no relationship between maternal haemoglobin levels and the levels of Down syndrome markers in either the first or second trimester. Biochemical marker levels do not need to be corrected for haemoglobin concentrations when used in screening for Down syndrome.

Study of placenta of children born with congenital malformations

The malformations in this study were observed in a series of 279,642 consecutive births of known outcome registered in our Registry of congenital anomalies. For each case, more than 50 factors included in the registration forms were studied. One of the factors studied was the placenta. For each malformed child, a control was chosen. Cases with maternal known factors impairing placenta function, i.e. vasculopathy and diabetes, were excluded. In each category of malformations studied, the malformed children were divided into isolated and non-isolated (multiple malformed) cases. The weight of placenta of isolated cases was not lower than the weight of placenta of the controls. In contrast, the weight of placenta of the cases with non-isolated malformations was lower than the weight of placenta of the controls and of the isolated cases, for all categories of malformations but gastroschisis and omphalocele. The mean weights at birth of the cases with multiple malformations were also lower than those of the controls. The human placenta discounts a principal functional part, the maternal blood in the intervillous space. Congenital malformations may interact with this function.