STUDY QUESTION: Is periconceptional maternal one-carbon (I-C) metabolism associated with embryonic morphological development in non-malformed ongoing pregnancies? SUMMARY ANSWER: Serum vitamin B12, red blood cell (RBC) folate and plasma total homocysteine (tHcy) are associated with embryonic development according to the Carnegie stages. WHAT IS KNOWN ALREADY: Derangements in maternal I-C metabolism affect reproductive and pregnancy outcomes, as well as future health of the offspring. STUDY DESIGN, SIZE, DURATION: Between 2010 and 2014, women with singleton ongoing pregnancies were enrolled in a prospective periconceptional cohort study. PARTICIPANTS/MATERIALS, SETTING, METHODS: A total of 234 pregnancies, including 138 spontaneous or IUI pregnancies with strict pregnancy dating and 96 pregnancies derived from IVF, ICSI or cryopreserved embryo transfer (IVF/ICSI pregnancies), underwent longitudinal transvaginal three-dimensional ultrasound (3D US) scans from 6+0 up to 10+2 weeks of gestation. Carnegie stages were defined using internal and external morphologic criteria in a virtual reality system. Maternal venous blood samples were collected at enrollment for serum vitamin B12, RBC folate and plasma tHcy assessment. Associations between biomarker concentrations and longitudinal Carnegie stages were investigated using linear mixed models. MAIN RESULTS AND THE ROLE OF CHANCE: We performed a median of three 3D US scans per pregnancy (range 1-5) resulting in 600 good quality data sets for the Carnegie stage annotation (80.5%). Vitamin B12 was positively associated with embryonic development in the total study population (β = 0.001 (95% CI: 0.000; 0.002), P < 0.05) and in the subgroup of strictly dated spontaneous pregnancies (β = 0.002 (95% CI: 0.001; 0.003), P < 0.05). Low vitamin B12 concentrations (-2SD, 73.4 pmol/l) were associated with delayed embryonic development by 1.4 days (95% CI: 1.3-1.4) compared with high concentrations (+2SD, 563.1 pmol/l). RBC folate was positively associated with Carnegie stages only in IVF/ICSI pregnancies (β = 0.001 (95% CI: 0.0005; 0.0015), P < 0.05). In this group, low RBC folate concentrations (-2SD, 875.4 nmol/l) were associated with a 1.8-day delay (95% CI: 1.7-1.8) in development compared with high concentrations (+2SD, 2119.9 nmol/l). tHcy was negatively associated with embryonic development in the total study population (β = -0.08 (95% CI: -0.14; -0.02), P < 0.01), as well as in the IVF/ICSI subgroup (β = -0.08 (95% CI: -0.15; -0.01), P < 0.05). High tHcy concentrations (+2SD, 10.4 μmol/l) were associated with a delay of 1.6 days (95% CI: 1.5-1.7) in embryonic development compared with low concentrations (-2SD, 3.0 μmol/l). LIMITATIONS, REASONS FOR CAUTION: The study was performed in a tertiary care center, resulting in high rates of folic acid supplement use and comorbidity that may reduce the external validity of our findings. WIDER IMPLICATIONS OF THE FINDINGS: In periconceptional care, maternal I-C biomarkers should be taken into account as predictors of embryonic morphological development. Combining embryonic size measurements with morphological assessment could better define normal embryonic development.

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Human Reproduction
Erasmus MC: University Medical Center Rotterdam

Parisi, F., Rousian, M., Koning, A., Willemsen, S., Cetin, I., & Steegers-Theunissen, R. (2017). Periconceptional maternal one-carbon biomarkers are associated with embryonic development according to the Carnegie stages. Human Reproduction, 32(3), 523–530. doi:10.1093/humrep/dew349