Doctors describe overweight and obesity as excessive fat accumulation that may impair health.
To distinguish between both concepts in adults is used body mass index (BMI). It is marked as a person’s weight in kilograms divided by the square of his height in meters (kg/m2).
For adult women, overweight and obesity are defined as follows:
- overweight is a BMI ≥ 25
- obesity is a BMI ≥ 30
Excessive fat deposition is associated with a variety of female fertility issues.
- Polycystic ovary syndrome (PCOS)
- Decreased oocyte quality
- Infertility treatment outcome
- Pregnancy complications
Polycystic ovary syndrome (PCOS)
In women, extra adipose tissue provokes polycystic ovary syndrome (PCOS), a highly prevalent endocrine female disorder.
PCOS is a group of symptoms that attacks the ovaries, which produce estrogen and progesterone — hormones that manage the menstrual cycle. The ovaries also release a small number of androgens (male hormones). Three main features of PCOS are:
- cyst growth in the ovaries
- increased male hormones
- menstrual irregularity
In PCOS, many tiny, fluid-filled cysts grow inside the ovaries. These cysts are follicles, each containing an immature egg that never develops ultimately to trigger ovulation. The reduction of ovulation modifies estrogen, progesterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels while increasing androgen levels.
Extra male hormones disrupt the menstrual cycle, leading to fewer periods than usual. Testosterone and other androgens above the norm can harm a womanʼs fertility.
Obese women with polycystic ovary morphology (PCOM) had a higher chance of developing PCOS than nonobese women with PCOM. Studies report that approximately 76% of women with PCOS have obesity.
Excessive weight is usually connected with ovulatory dysfunction.
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH), produced in the pituitary gland, regulate ovulation. FSH stimulates the ovary to release a follicle that contains an egg, and then LH triggers the ovary to free a mature egg.
The mechanism of anovulation in obesity remains unclear. Insulin resistance is enhanced in obese women. It is proved that insulin stimulates estrogen production, causing inappropriate estrogen levels in the developing follicle. By augmenting LH effects, insulin suppresses the final differentiation of follicle cells. Thus, premature luteinization and follicular arrest lead to menstrual cycle disturbances and obesity-related anovulation.
Even with regular menstrual cycles, obese women show diminished LH amplitude, sometimes followed by prolonged folliculogenesis and decreased luteal progesterone levels. Thus, the ovulation process is disturbed.
In addition, increased adipokines, especially leptin, generated in adipose tissue can directly inhibit ovarian function.
Decreased oocyte quality
Obesity alters oocyte morphology. Blastocysts developed from oocytes of obese women are minor, include fewer cells, with higher triglyceride content, lower glucose consumption, and changed amino acid metabolism compared with embryos from normal-weight women (BMI <24.9 kg/m2)10.
Moreover, obesity causes follicle apoptosis, oxidative stress in oocyte complexes, oocytes division defects, poor embryo development with reduced survival, and abnormal growth.
Infertility treatment outcome
Excessive fat accumulation causes destroying of embryo quality during in vitro fertilization (IVF) in women younger than 35 years old. Some studies proved that obesity reduces fertilization. Women with a BMI >25 kg/m2 have smaller oocytes that are less likely to complete post-fertilization.
Obese women undergoing IVF also have a weakened chance of clinical pregnancy compared with normal-weight women. A systematic review represents that overweight women have a 10% lower live birth rate than women of average weight during IVF. According to recent studies, obesity reduces embryo implantation.
Obesity is associated with higher doses of medications to influence ovulation or stimulate ovaries for IVF. When hormones gonadotropins are used for ovulation induction, overweight correlates with an increased quantity of administered FSH, fewer mature follicles, and a decreased chance of ovulation.
During pregnancy, obese women have an enormously higher risk of complications, including preeclampsia, gestational diabetes, preterm delivery, and miscarriage.
Preeclampsia is defined as a condition caused by high blood pressure and significant amounts of protein in the urine. Preeclampsia also increases the chance of cesarean section.
When a woman faces gestational diabetes, the chances of a baby’s overweight are increased.
The connection between obesity and miscarriage has been found in both natural and assisted fertilization. Suggested mechanisms are endometrial damages, alterations in embryo quality, and uterine receptivity.
Studies confirm the associations between maternal obesity and congenital anomalies such as neural tube defects, cardiovascular abnormalities, cleft lip and palate, hydrocephalus, etc..
As a result, the obesity epidemic redounds to increasing fertility difficulties, negatively impacting womenʼs and their offspring’s health.
- World Health Organization
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