There is evidence that some mothers of infants with Down's syndrome have abnormal metabolism of folate and methyl, as well as mutations in folate genes, which are features that are also seen in neural-tube defects. In the families at risk of neural-tube defects, there were a total of 11 pregnancies affected by Down's syndrome in 1492 at-risk pregnancies (compared with 1·87 expected on the basis of maternal age), which was a significant increase. In the families at risk of Down's syndrome, there were seven neural tube defect pregnancies in 1847 at risk, compared with 1·37 expected. In this study, we provide direct evidence of a link between Down's syndrome and neural tube defects. Folate supplementation before conception has the potential to reduce the frequency of Down's syndrome.
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2803%2913080-2/abstract
Healthy men who report lower levels of the nutrient folate in their diets have higher rates of chromosomal abnormalities in their sperm. After accounting for factors such as age, alcohol use and medical history, the researchers found that men reporting the highest intake of folate had 19 percent lower rates of sperm with abnormal numbers of chromosomes than men with moderate folate intake, and 20 percent lower rates compared with men in the low folate intake group. An estimated 1 to 4 percent of a healthy male's sperm have abnormal numbers of chromosomes, or aneuploidy, that are caused by errors during cell division (meiosis) in the testis. If these abnormal sperm fertilize a normal egg, there would either be a miscarriage or a fetus with a chromosomal disorder such as trisomy, in which cells have three rather than the normal two copies of a given chromosome. The researchers were not able to determine a link between sperm aneuploidy and the other nutrients examined, such as zinc, calcium, beta-carotene and other vitamins.
http://www.sciencedaily.com/releases/2008/03/080319193036.htm
A significantly greater proportion of women with abnormal fetal karyotype had elevated baseline serum FSH (> or =15 mIU/mL [RIA] or 10 mIU/mL [Immulite]) and/or estradiol > or = 50 pg/mL) compared with women of normal fetal karyotype.
http://www.fertstert.org/article/S0015-0282%2898%2900525-1/abstract
Exposure to the contraceptive pill at/or around the occasion of conception can affect the risk of Down Syndrome. For young mothers this exposure can increase the risk, whereas for older mothers it can decrease the risk.
http://www2.hud.ac.uk/hhs/ld/down.pdf
Younger mothers (<35 years) who smoke and have meiotic II error are at an increased risk of having children with Down syndrome. The combined use of cigarettes and oral contraceptives increased the risk even further.
http://www.cdc.gov/ncbddd/bd/ds.htm
Women who reported surgical removal of all or part of an ovary or congenital absence of one ovary were significantly more likely to have delivered a child with Down Syndrome than were women who did not report a reduced ovarian complement (odds ratio 9.61). Because others have observed that women who have had an ovary removed exhibit elevated levels of FSH and similar hallmarks of advanced maternal age, our finding suggests that the physiological status of the ovary is key to the maternal-age effect.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1378004/pdf/10733467.pdf
An earlier cessation of reproductive life, brought on by unilateral ovariectomy in CBA females, resulted in the earlier onset of irregular cyclicity and an earlier rise in aneuploidy. The results could not be explained on the basis of the "production line" hypothesis.
http://www.springerlink.com/content/k7r0420774784661/
Compared with women <25 years of age, women > or = 40 years old had an odds ratio of 5.2 for maternal meiosis 1 (MMI) errors (occur between birth and month before conception) and 51.4 for maternal meiosis 2 (MMII) errors (occur during follicular phase just prior to conception). Birth-prevalence rates for women > or = 40 years old were 4.2/1000 births for MMI errors and 1.9/1000 for MMII errors. These results support an association between advanced maternal age and both MMI and MMII errors. The association with MI does not pinpoint the timing of the error; however, the association with MII implies that there is at least one maternal-age related mechanism acting around the time of conception.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1914585/pdf/ajhg00016-0193.pdf
The authors produced trisomic and triploid embryos by mating hamster females approximately 1 hr before estimated ovulation and subsequently submitting them to low-pressure atmospheres equivalent to those found at mountain altitudes for 6 hr. During hypoxic exposures in the low-pressure chamber, the continuous monitoring of pH levels--both subcutaneously and intramuscularly--registered pH decreases from inital values as high as 7.6 to below 6.9. These findings indicate that trisomies in some embryos and triploidies in others have their origin in different, but related mechanisms involving maternal pH imbalances between ovulation and fertilization.
http://www.ncbi.nlm.nih.gov/pubmed/7369790
Polyploidy and aneuploidy in hamster embryos are produced as manifestations of pregnancy wastage in surviving young when the interval between the estimated time of ovulation and copulation and hence fertilization is progressively increased. Significant delays resulted in triploidy in runted embryos, and the sporadic occurrence of mosaic aneuploidies.
http://www.ncbi.nlm.nih.gov/pubmed/5032353
Menstrual Cycle and Birth Defects
For a concise list of qualities found to affect one's risk of miscarriage, see: Causes of Miscarriage