Age determination enhanced by embryonic foot bud and foot plate measurements in relation to Carnegie stages, and the influence of maternal cigarette smoking

OUP accepted manuscript

STUDY QUESTION

Is periconceptional maternal smoking associated with embryonic morphological development in ongoing pregnancies?

SUMMARY ANSWER

Smoking during the periconceptional period is associated with a delayed embryonic morphological development which is not fully recuperated beyond the first trimester of pregnancy.

WHAT IS KNOWN ALREADY

Smoking during pregnancy decreases prenatal growth, increasing the risk of preterm birth, small for gestational age (GA) and childhood obesity.

STUDY DESIGN, SIZE, DURATION

Between 2010 and 2018, 689 women with ongoing singleton pregnancies were periconceptionally enrolled in a prospective cohort study with follow-up until 1 year after delivery.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Between 7 + 0 and 10 + 3 weeks, GA serial three-dimensional transvaginal ultrasound scans were performed. Embryonic morphological development as assessed by the Carnegie developmental stages was evaluated using Virtual Reality techniques. In the absence of fetal morphology classification methods beyond the embryonic period, fetal ultrasound measurements at around 20 weeks’ GA, and birth weight were used to assess fetal growth. Linear mixed models were used to evaluate the association between smoking and the Carnegie stages. Regarding first-trimester morphological development, we additionally stratified our findings for mode of conception. Multiple linear regression models were used to study the association between smoking, fetal growth and birth weight. To investigate to which extent delayed embryonic morphological development mediated the effect of smoking, contemporary mediation analysis was used. Adjustments were made for potential confounders and other covariates.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 689 singleton ongoing pregnancies were included and 1210 Carnegie stages were determined. Maternal periconceptional smoking represented by the number of cigarettes/day was associated with a slight non-significant delay of the Carnegie stages (β_{cigarettes/day} = −0.058, 95% CI −0.122; 0.007, P = 0.080). Smoking of ≥10 cigarettes/day showed the strongest association (β_{≥10 cigarettes/day} = −0.352, 95% CI −0.648; −0.057, P = 0.019), as reflected by a 0.9-day delay in reaching the final Carnegie stage. Stratification for mode of conception showed a stronger negative association between the number of cigarettes/day in the IVF/ICSI group (β_{cigarettes/day} = −0.126, 95% CI −0.200; −0.051, P = 0.001) compared to naturally conceived pregnancies (β_{cigarettes/day} = 0.009, 95% CI −0.093; 0.111, P = 0.867). In the IVF/ICSI group, periconceptional smoking of ≥10 cigarettes/day was associated with in a 1.6 day delay in reaching the final Carnegie stage (β_{≥10 cigarettes/day} = −0.510, 95% CI −0.834; −0.186, P = 0.002). In the second trimester, periconceptional smoking was associated with a smaller femur length (β_{cigarettes/day} = −0.077, 95% CI −0.147; −0.008, P = 0.029) and a larger head circumference (β_{1–9 cigarettes/day} = 0.290, 95% CI 0.065; 0.514, P = 0.012). Smoking was associated with a lower birth weight, with a dose-response effect (β_{cigarettes/day} = −0.150, 95% CI −0.233; −0.068, P < 0.001). Furthermore, using the unadjusted model, 40–60% of the association between smoking and fetal ultrasound parameters and 6.3% of the association between smoking and birth weight can be explained by a delayed embryonic morphology.

LIMITATIONS, REASONS FOR CAUTION

The study population was recruited from a tertiary referral center. Smoking habits were explored using self-reported questionnaires and checked for consistency by trained researchers.

WIDER IMPLICATIONS OF THE FINDINGS

This study shows that the association of periconceptional maternal smoking and human morphological development can already be detected early in the first trimester of pregnancy using embryonic morphology as outcome. One of the key messages of this study is that the delay, or dysregulation, in embryonic morphology is associated with allometric growth reflected by smaller fetal measurements at 20 weeks gestation and lower weight at birth. The delay in embryonic morphology, measured in early pregnancy, cannot be recuperated during the pregnancy. The results of this study emphasize the importance of smoking intervention programs prior to conception. More research is warranted to assess the association between periconceptional smoking cessation and embryonic development.

STUDY FUNDING/COMPETING INTEREST(S)

The work was funded by the Department of Obstetrics and Gynaecology, Erasmus MC, University Medical Centre, Rotterdam, The Netherlands. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

A revisit of the fetal foot length and fetal measurements in early pregnancy sonography

Objectives

To present the fetal measurements in relation to the foot length at 10–16 weeks gestation on antenatal ultrasound.

Materials and methods

We reviewed the fetal measurements in 47 scans performed at 10–16 weeks gestation in women attending routine antenatal care. The fetal measurements and measurement ratios were examined in relation to the foot length.

Results

The fetal biparietal diameter, head circumference, abdominal circumference, femur length and foot length increase linearly with the gestational age at 10–16 weeks gestation. The correlation between fetal foot length and fetal biparietal diameter, head circumference, abdominal circumference and femur length are better than with the crown rump length. The femur length to foot length ratio and the femur length to abdominal circumference ratios increase with the gestational age in an inverse relationship throughout the same period.

Conclusion

Fetal foot length is an accurate estimate of the gestational age in early pregnancy. Compared with crown rump length, the correlation between foot length and other fetal measurements is better. The fetal measurements ratios are gestational age dependent between 10–16 weeks. Gestational age specific ratio should be used in this period.

Proliferation of germ cells and somatic cells in first trimester human embryonic gonads as indicated by S and S+G2+M phase fractions

OBJECTIVES

The number of germ cells and somatic cells in human embryonic and foetal gonads has previously been estimated by stereological methods, which are time- and labour-consuming with little information concerning cell proliferation. Here, we studied whether flow cytometry could be applied as an easier method, also enabling estimation of the fraction of cells in S or S+G(2)+M (SG(2) M) cell-cycle phases as indicators of cell proliferation.

METHODS

Cell suspensions from 35 human embryonic gonads at days 37 to 68 post-conception (pc) were immunomagnetically sorted into C-KIT positive (germ) cells and negative (somatic) cells. They were stained for DNA content and analysed by flow cytometry. S and SG(2) M fractions could be measured for 13 of the female and 20 of the male gonads. The number of cells was estimated using fluorescent reference beads.

RESULTS

During the period from 37 to 68 days pc, female germ and somatic cells had a stable S and SG(2) M fractions indicating steady growth of both subpopulations, whereas they decreased in both male germ and somatic cells. The number of germ and somatic cells estimated by flow cytometry was significantly lower than in stereological estimates, suggesting loss of cells during preparation.

CONCLUSIONS

Cell proliferation as indicated by S and SG(2) M fractions could be estimated specifically for primordial germ and somatic cells. Estimation of total number of germ and somatic cells was not feasible.

Human primordial germ cells migrate along nerve fibers and Schwann cells from the dorsal hind gut mesentery to the gonadal ridge

The aim of this study was to investigate the spatiotemporal development of autonomic nerve fibers and primordial germ cells (PGCs) along their migratory route from the dorsal mesentery to the gonadal ridges in human embryos using immunohistochemical markers and electron microscopy. Autonomic nerve fibers in the dorsal mesentery, the pre-aortic and para-aortic plexuses and in the gonadal ridge were stained for beta III tubulin, neuron specific enolase and the glia fibrillary acidic protein. Electron microscopy demonstrated the presence of neurofilaments and neurotubules in these nerve fibers and their intimate contact with PGCs. PGCs expressed GAGE, MAGE-A4, OCT4 and c-Kit. Serial paraffin sections showed that most PGCs were located inside bundles of autonomic nerve fibers with the majority adjacent to the most peripheral fibers (close to Schwann cells). We also show that both nerve fibers and PGCs arrive at the gonadal ridge between 29 and 33 days pc. In conclusion, our data suggest that PGCs in human embryos preferentially migrate along autonomic nerve fibers from the dorsal mesentery to the developing gonad where they are delivered via a fine nerve plexus.

Expression of the homeobox genes OTX2 and OTX1 in the early developing human brain

In rodents, the Otx2 gene is expressed in the diencephalon, mesencephalon, and cerebellum and is crucial for the development of these brain regions. Together with Otx1, Otx2 is known to cooperate with other genes to develop the caudal forebrain and, further, Otx1 is also involved in differentiation of young neurons of the deeper cortical layers. We have studied the spatial and temporal expression of the two homeobox genes OTX2 and OTX1 in human fetal brains from 7 to 14 weeks postconception by in situ hybridization and immunohistochemistry. OTX2 was expressed in the diencephalon, mesencephalon, and choroid plexus, with a minor expression in the basal telencephalon. The expression of OTX2 in the hippocampal anlage was strong, with no expression in the adjacent neocortex. Contrarily, the OTX1 expression was predominantly located in the proliferative zones of the neocortex. At later stages, the OTX2 protein was found in the subcommissural organ, pineal gland, and cerebellum. The early expression of OTX2 and OTX1 in proliferative cell layers of the human fetal brain supports the concept that these homeobox genes are important in neuronal cell development and differentiation: OTX1 primarily in the neocortex, and OTX2 in the archicortex, diencephalon, rostral brain stem, and cerebellum.