Postponed pregnancy is referred to postponement of childbearing to a higher age (over 35 years), which may involve higher risk of infertility for the woman and/or chromosomal abnormalities for the child.
Female fertility is affected by age (Pic. 1). Age is thus a major fertility factor for women. After puberty, female fertility increases and then decreases, with advanced maternal age c ausing an increased risk of female infertility. In humans, a woman's fertility peaks in the early and mid-20s, after which it starts to decline slowly.
Although about 1 million oocytes are present at birth in the human ovary, only about 500 (about 0.05%) of these ovulate, and the rest are wasted (ovarian follicle atresia). In terms of ovarian reserve, a typical woman has 12% of her reserve at age 30 and has only 3% at age 40. 81% of variation in ovarian reserve is due to age alone, making age the most important factor in female infertility.
The decline in ovarian reserve appears to occur at a constantly increasing rate with age, and leads to nearly complete exhaustion of the reserve by about age 51 (menopause). As ovarian reserve and fertility decline with age, there is also a parallel increase in pregnancy failure and meiotic errors resulting in chromosomally abnormal conceptions.
Currently, postponing motherhood can be considered a worldwide phenomenon - over the last 30 years, although birth rates have been decreasing, the average mother's age has been gradually increasing. Numerous factors contribute to this scenario, such as women's stronger presence in the job market, an increase in education and career opportunities for women, and the development of reproductive medicine with regards to family planning and contraceptive methods.
The risk of the mother dying before the child becomes an adult increases by more advanced maternal age. Advanced maternal age continues to be associated with a range of adverse pregnancy outcomes including low birth weight, pre-term birth, stillbirth, unexplained fetal death, and increased rates of Caesarean section.
On the other hand, advanced maternal age is associated with a more stable family environment, higher socio-economic position, higher income and better living conditions, as well as better parenting practices, but it is more or less uncertain whether these entities are effects of advanced maternal age, are contributors to advanced maternal age, or common effects of a certain state such as personality type.
Advanced maternal age is associated with adverse reproductive effects such as increased risk of infertility due to decline in ovarian reserve, and that the children have chromosomal abnormalities. The corresponding paternal age effect is less pronounced.
Preeclampsia is refered to pregnancy complication characterized by high blood pressure and signs of damage to another organ system, most often the liver and kidneys. Advanced maternal age is one of the risk factors of preeclampsia. Although preeclampsia does not have the direct impact on fertility, the presence of preeclampsia, regardless of its severity, entails increased fetal and maternal risk. Research suggests the risk of having preeclampsia again is approximately 20%.
Postponed pregnancy and thus associated advanced maternal age is an established risk factor for gestational diabetes mellitus (GDM), nevertheless there is no consesnsus on the age above there is increased risk of GDM. Gestational diabetes is a condition of high blood sugar level that begins or is first recognised during pregnancy.
Usually, gestational diabetes resolves after the birth of the baby with no direct on fertility itself. The main diabetes complication (including gestational diabetes) related to pregnancy is macrosomia - or a big baby (higher than the 90th percentile in birth weight). Sometimes these babies are not able to pass through the birth canal, so there are higher incidences of caesarean sections, and sometimes it is necessary to induce labor early.
Ectopic pregnancy refers to the implantation of a embryo outside of the uterine cavity, most often in fallopian tube. The risk of ectopic pregnancy increases with advanced maternal age, with age over 35 years being a significant risk factor. Fertility following ectopic pregnancy depends upon several factors, the most important of which is a prior history of infertility. The treatment choice does not play a major role.
In comparison with younger women, studies have shown that among those 35 and above, there are more miscarriages and abortions, and a higher risk for perinatal mortality, ectopic pregnancy, low vitality of newborns, low weight at birth, preterm birth, and fetuses who are small for their gestational age. A woman's risk of having a baby with chromosomal abnormalities increases with her age. Down syndrome (Pic. 2) is the most common chromosomal birth defect.
Social egg freezing
Social egg freezing is common term for the preservation by freezing (cryopreservation) and storage of human oocytes for later personal use or donation.
The technology is a modification of in vitro fertilisation (IVF), where women inject themselves on a daily basis with very large doses of fertility hormones so that they produce many eggs in a single cycle, known as super ovulation. These eggs are invasively extracted from the ovaries, and rather than being fertilised with sperm and re-transplanted as with IVF, the unfertilised eggs are frozen.
With egg freezing for social reasons, the women undergoing this invasive procedure are perfectly healthy, their only condition often being desperation. Health professionals have a good understanding of the risks involved - vaginal bleeding, soreness, bruising and cramping, and in rare cases, a potentially lethal condition called ovarian hyperstimulation syndrome (OHSS).
Family planning can help prevent getting postponed pregnancy, thus helping to avoid the complications associated with advanced maternal age.
In humans, the fertility in female declines slowly from the age of 30 years. Embryo implanting ability and survival start declining gradually after 30 years of age, but by more than two thirds after 40 years and in younger women with reduced ovarian reserve.
Older uterus or ageing oocytes
In cycling women >40 years, a disturbance in follicular recruitment but not in luteal function or endometrial maturation has been observed and its possible role in the decline in fertility with ageing suggested.
While decline in the frequency of intercourse is one of the reasons, reduction in the quality of either the embryos arising from ageing oocytes due to higher incidence of oocyte aneuploidy (abnormal number of chromosomes in a cell) or the older uterus have been implicated as the probable causes.
Controversy still exists about which one of these is the main cause or whether both of them play a role together. While the suboptimal quality (competence for fertilization) of the ageing oocytes and/or older uterus may be responsible for the age-related decline in female fertility, it is not clear why the functional quality of the uterus or the oocytes declines with increasing age.
Elsewhere, it has been suggested that age-related changes in the ovary account for most of the decline in fertility. Oocytes, which originate in the fetal life, decline in numbers and quality with age. The endocrine function of the ovary also declines with age leading to dysfunction of the neuro endocrine axis (cooperation of nervous system with endocrine).
The uterine lining may change due to the age-related endocrine dysfunction thereby losing its ability to support implantation and growth of the embryo. The frequency of chromosomal anomalies in abortuses increases in parallel with the age-related rise in the incidence of spontaneous abortions. That oocyte aneuploidy is one major reason for low pregnancy rates in older women, is suggested by the higher pregnancy rate in this group where young donor oocytes are used.
With increase in age, the number of retrieved oocytes decreased. Moreover, the majority of the studies have suggested a decrease in the quality of the oocytes as the main cause of the age-related decline in female fertility, contribution by the uterus also remains a possibility.
A substantial drop in the ongoing pregnancy rate per embryo transfer has been observed in women undergoing assisted reproduction, 48.8% in women aged <30 years to 13.6% in women aged >42 years). Embryo implantation rate also declines in a linear fashion, from 29% in women <34 years to approximately 5% at age 42. The reduced implantation rate in older women is apparently independent of the magnitude of their stimulation response.
Control during the prenatal period, adequate care during childbirth, and childbirth itself make maternal and perinatal prognoses similar to those of younger pregnant women, and positive results are expected from these pregnancies.