Conception 2012

[Zulema Estabrooks]

Mostof the time, you won't know the exact day you got pregnant. Your doctor will count the start of your pregnancy from the first day of your last menstrual period. That's about 2 weeks ahead of when conception happens.

Each month inside your ovaries, a group of eggs starts to grow in small, fluid-filled sacs called follicles. Eventually, one of the eggs erupts from the follicle (ovulation). It usually happens about 2 weeks before your next period..

After the egg leaves the follicle, the follicle develops into something called the corpus luteum. The corpus luteum releases a hormone that helps thicken the lining of your uterus, getting it ready for the egg.

After the egg is released, it moves into the fallopian tube. It stays there for about 24 hours, waiting for a single sperm to fertilize it. All this happens, on average, about 2 weeks before your next period.

If no sperm is around to fertilize the egg, it moves through to the uterus and disintegrates. Your hormone levels go back to normal. Your body sheds the thick lining of the uterus, and your period starts.

The fertilized egg stays in the fallopian tube for about 3 to 4 days. But within 24 hours of being fertilized, it starts dividing fast into many cells. It keeps dividing as it moves slowly through the fallopian tube to the uterus. Its next job is to attach to the lining of uterus. This is called implantation.

Some women notice spotting (or slight bleeding) for 1 or 2 days around the time of implantation. The lining of the uterus gets thicker and the cervix is sealed by a plug of mucus. It will stay in place until the baby is ready to be born.

A pregnancy hormone known as hCG is in your blood from the time of implantation. This is the hormone detected in a pregnancy test. Some home pregnancy tests can detect hCG as soon as 7 days after ovulation.

COVID-19 vaccination does not affect the chances of conceiving a child, according to a study of more than 2,000 couples that was funded by the National Institutes of Health. Researchers found no differences in the chances of conception if either male or female partner had been vaccinated, compared to unvaccinated couples. However, couples had a slightly lower chance of conception if the male partner had been infected with SARS-CoV-2 within 60 days before a menstrual cycle, suggesting that COVID-19 could temporarily reduce male fertility. The study was conducted by Amelia K. Wesselink, Ph.D., of Boston University, and colleagues. It appears in the American Journal of Epidemiology.

Researchers analyzed data from the Pregnancy Study Online (PRESTO), an internet-based prospective cohort study of U.S. and Canadian couples trying to conceive without fertility treatment. PRESTO is led by Lauren A. Wise, Sc.D., of Boston University.

Study participants identified as female and were 21 to 45 years old. They completed a questionnaire on their income and education levels, lifestyle, and reproductive and medical histories, including whether or not they were vaccinated against COVID-19 and whether they or their partners had ever tested positive for SARS-CoV-2. They also invited their male partners aged 21 or older to complete a similar questionnaire. Female partners completed follow-up questionnaires every eight weeks until they became pregnant, or up to 12 months if they did not.

The investigators found no major differences in conception rates per menstrual cycle between unvaccinated and vaccinated couples in which at least one partner had received at least one dose of the vaccine.

Results were similar when the investigators looked at factors that could potentially influence the results, such as whether study participants or their partners received one or two doses of a vaccine, the type of vaccine they received, how recently they were vaccinated, whether they were American or Canadian, whether they were health care workers, or they were couples without a history of infertility.

Overall, testing positive for SARS-CoV-2 infection was not associated with a difference in conception. However, couples in which the male partner had tested positive within 60 days of a given cycle were 18% less likely to conceive in that cycle. There was no difference in conception rates for couples in which the male partner had tested positive more than 60 days before a cycle, compared to couples in which the male partner had not tested positive.

Fever, known to reduce sperm count and motility, is common during SARS-CoV-2 infection and so could explain the temporary decline in fertility the researchers observed in couples in which the male partner had a recent infection. Other possible reasons for a decline in fertility among male partners who recently tested positive could be inflammation in the testes and nearby tissues and erectile dysfunction, all common after SARS-CoV-2 infection. The researchers noted that this short-term decline in male fertility could potentially be avoided by vaccination.

The researchers concluded that their results suggest that vaccination against COVID-19 had no harmful association with fertility. Vaccination against COVID-19 also could help avert the risks that SARS-CoV-2 infection poses for maternal and fetal health.

About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): NICHD leads research and training to understand human development, improve reproductive health, enhance the lives of children and adolescents, and optimize abilities for all. For more information, visit

About the National Institutes of Health (NIH):NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.

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In experimental animals, maternal diet during the periconceptional period influences the establishment of DNA methylation at metastable epialleles in the offspring, with permanent phenotypic consequences. Pronounced naturally occurring seasonal differences in the diet of rural Gambian women allowed us to test this in humans. We show that significant seasonal variations in methyl-donor nutrient intake of mothers around the time of conception influence 13 relevant plasma biomarkers. The level of several of these maternal biomarkers predicts increased/decreased methylation at metastable epialleles in DNA extracted from lymphocytes and hair follicles in infants postnatally. Our results demonstrate that maternal nutritional status during early pregnancy causes persistent and systemic epigenetic changes at human metastable epialleles.

Eight of the 13 biomarkers, and two derived variables (BET:DMG and SAM:SAH) showed significant differences between seasons of conception (Fig. 1a and Supplementary Table 2). Maternal periconceptional concentrations of FOL, B2, MET, BET and the SAM:SAH and BET:DMG ratios were higher in the rainy season, and concentrations of ACTB12, DMG, HCY and SAH were lower. Biomarker-specific seasonality in the main and indicator groups are illustrated in Fig. 1b and Supplementary Fig. 1.

(a) Heatmap of seasonal variation in maternal plasma biomarker concentrations at the time of conception. Columns correspond to pregnant women (main group), grouped according to season of conception. Colours represent deviation from all season mean biomarker concentrations, calculated as z-scores. Biomarkers are ranked by mean seasonal difference (Supplementary Table 2), with the greatest increment in the rainy versus dry season (BET:DMG) at the top, and the greatest decrement (SAH) at the bottom. Analysis of variance P-values: *

(a) Percent methylation at the six MEs in PBL of infants conceived in the dry or rainy season. Median % methylation is consistently higher in infants conceived in the rainy season. (b) Mean PBL methylation z-score across the six MEs is significantly higher in infants conceived in the rainy season. (c) Percent methylation at the six MEs in HF of infants conceived in the dry or rainy season; the overall pattern of methylation is similar to that observed in PBL, as is the seasonal difference in mean methylation z-score (d). Box plots represent the median (horizontal line) and interquartile range (box) of the indicated distribution. The whiskers extend from the top/bottom of the box to the highest/lowest data value that is within 1.5. Asterix represents interquartile range of the box. Data beyond the whiskers are plotted as individual points. PBL, peripheral blood lymphocyte; Oneway analysis of variance P-values: *

Evidence is accumulating that environmental factors during early-life have long-term effects on later health outcomes and that these processes reflect epigenetic responses to periconceptional exposures17. Our data represent first-in-human confirmation that the maternal blood biomarker status of substrates and cofactors required for methyl-donor pathways, measured around the time of conception, predicts the methylation patterns of MEs in offspring. Increased maternal BMI was also predictive of decreased systemic infant DNA methylation at MEs. This finding is potentially of global significance and is the subject of further studies in which we are attempting to distinguish possible effects driven by total adiposity and/or dynamic changes in energy balance. Further research beyond the current set of MEs and the follow-up of infants from this study is also ongoing.

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