ADVANCED MATERNAL AGE AND PREGNANCY RISKS

There is currently an increasing trend towards delay childbearing across the world. Among the reasons are delay due to longer schooling, late marriage, shift in life priority, financial security, availability of contraception and women exercising their choices.  The consequence of this shift has led to more elderly pregnant mothers.

The commonly accepted definition of advanced maternal age (elderly) is 35 years or more. Studies have shown that pregnancy in this group of women is associated with a higher complication risk to both the mother and baby. Women should be supported in their decisions of whether to have children or not and when to plan childbearing. They should also be aware that the fertility and pregnancy outcomes change with age. For these reasons, women are encouraged to consider having families during the period of optimum fertility.

Pregnancy risks

Maternal age has been shown to affect pregnancy from conception to delivery. Biologically, the best period for pregnancy is between 20–35 years of age. The spontaneous conception rate is 75% in women aged 30 compared to 66% in those aged 35 years old (Leridon 2004). The pregnancy rate in elderly women is lower due to poorer egg quality associated with aging.  There is also a higher risk of spontaneous miscarriage. The reported miscarriage rate at 22 years old is 8.2%, but increases to 20% among women at 35 years of age.

Elderly mother has an increased risk of fetal chromosomal abnormalities and congenital anomalies. The risk of Down syndrome, the commonest cause of mental retardation is significantly increased from 1 in 1000 when the pregnant woman is 25 years of age compared to 1 in 250 at 35 years.

There is also a higher association of preterm birth, small for gestational age (small baby and intrauterine growth restriction, IUGR) among elderly mothers. The preterm delivery may be unexplained or iatrogenic, due to intervention following maternal complications (see below). Elderly mother may be associated with poorer placental perfusion or transplacental flux of nutrients. This led to an increased likelihood of a small for gestational age baby.  All these complications are associated with a higher neonatal intensive care unit admission and higher morbidity.

 

Increase perinatal morbidity and mortality

The risk of stillbirth (fetal demise after 28weeks gestation) is significantly higher in older women, partly due to the risks of aneuploidy (chromosomal anomalies) and fatal congenital anomalies.  The increased incidence of small for gestational age babies in the older women further contributes to the increased stillbirth rate.

 

Maternal complications

Older women are more likely to have pre-existing medical disorders such as diabetes mellitus or hypertension, which further complicate the pregnancy. There is an increased incidence of antepartum haemorrhage, malpresentation, pre-eclampsia and gestational diabetes mellitus.  All these complications lead to a higher operative vaginal delivery and Caesarean section.

 

Conclusions

Pregnant women aged ≥35 years are at increased risk of complications in pregnancy compared with younger women. Although women should be supported in their life choices, they should be aware of the possible problems that older mothers may encounter. Adherent to frequent antenatal visits, under an experienced obstetrician and increased fetal surveillance are some measures that may help to ensure a better outcome.

 

References

  1. Huang L et al., CMAJ 2008.
  2. Leridon H. Human Reproduction 2004
  3. RCOG statement on later maternity age 2009

 

FERTILITY DECLINE WITH INCREASING MATERNAL AGE

Fertility is defined as the capacity to produce a child.  It is generally observed that 80% of couple will conceive in the first six months of attempting pregnancy (Gnoth 2003).  The monthly fecundity (the probability of pregnancy per month) is greatest in the first 3 months. The fertility rate is reduced by half among women in their late 30s compared to women in their early 20s (Dunson DB 2004).   This proved that age alone is the most important predictor of fertility.

Studies has shown that the pregnancy rate was 74% in women younger than 31 years compared to 62% for women ages 31-35 years and 54% for women older than 34 years of age.  Even with state of art IVF technology, the livebirth rate for younger than 35years was 41.5%, compared to at  12.1% at 40-44 years old.  The fertility rate decreases with increasing maternal age.

 

Reasons for a reduced fertility rate

The numbers of eggs in the woman’s ovaries are finite. It decreases naturally and progressively with age.  The total number of eggs is approximately 1 million at birth, 500,000 at puberty and is reduced to 1000 at menopause. The availability of eggs is one of the essential process of conception.  Fecundity defined as ability to conceive, decrease gradually but significantly at age of 32, then rapidlyly after age of 37.

Besides this natural loss, there is also a deterioration of egg quality as demonstrated by increasing FSH and decreasing AMH.  The risks of other disorders associated with ageing such as fibroid, tubal disease and endocrine condition may adversely affect the woman’s fertility.

 

Increase miscarriage rate in elderly mother  

Early pregnancy loss has also showed an increasing trend with advance maternal age.  This is partly due to increase in abnormal chromosome (aneuploidy), especially autosome trisomies.  The incidence of spontaneous miscarriage is 10% in women younger than 30 years; 20% in 41-42 years and 36.6% in older than 42 years

 

Conclusion

Women should be aware of the effect of age on fertility, should they choose to delay starting a family.  Given the decline in fertility, increase in pregnancy loss and pregnancy risk with aging, women older than 35 years should seek early medical attention if they fail to conceive after 6 months of attempting pregnancy.  For women who are older than 40 years, immediate evaluation and treatment are warranted.

 

Reference

Dunson DB et al., Am J Obstet Gynecol 2004

Gnoth C et al., Human Reproduction 2003