Anorexia Nervosa (AN) is an eating disorder defined by severe restriction of energy intake, resulting in an abnormally low body weight. This persistent undernourishment forces the body into a survival mode that shuts down non-essential biological processes. The reproductive system is one of the first systems significantly affected by this extreme energy deficit. The condition frequently impairs reproductive capability, often leading to a temporary state of infertility.
How Energy Deficit Halts Reproduction
The primary mechanism linking Anorexia Nervosa to infertility is a prolonged state of negative energy balance. The body interprets this nutritional deprivation as starvation and conserves energy for survival functions like breathing and circulation. Reproduction is categorized as non-essential and is therefore temporarily halted to divert resources elsewhere. This protective shutdown is signaled by the sharp reduction in leptin, a hormone produced by fat cells, which communicates low stored body fat to the brain. Low leptin levels signal the hypothalamus that the body is too malnourished to support a pregnancy, preventing the hormonal cascade required for ovulation.
Disrupting the Reproductive Hormone Axis
The biological mechanism for infertility in Anorexia Nervosa is classified as Hypothalamic Amenorrhea, a condition where the brain stops signaling the ovaries. This disruption involves the intricate communication network known as the Hypothalamic-Pituitary-Ovarian (HPO) axis. Under severe nutritional stress, the hypothalamus suppresses the pulsatile release of Gonadotropin-releasing hormone (GnRH).
GnRH travels to the pituitary gland to stimulate the release of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). When GnRH pulses are suppressed due to the energy deficit, the output of LH and FSH dramatically decreases, often regressing to a pattern similar to that seen before puberty. These hormones normally stimulate the ovaries to develop follicles and produce sex hormones like estrogen and progesterone. Without adequate stimulation, the ovaries become dormant, failing to mature an egg or produce the estrogen necessary for a menstrual cycle.
This lack of ovulation and subsequent absence of menstruation (amenorrhea) is the physical manifestation of infertility in AN. High levels of the stress hormone cortisol, often elevated in AN, also contribute to the suppression of the HPO axis.
Restoring Fertility After Recovery
Infertility resulting from Anorexia Nervosa is frequently reversible, requiring sustained recovery from the eating disorder. The primary requirement for restoring reproductive function is achieving and maintaining a healthy body weight and body composition. For many individuals, this means reaching a weight that is approximately 92% of their ideal body weight. The resumption of a regular menstrual cycle is the most common indicator that the HPO axis has reactivated and fertility is returning.
Menstrual cycles may not immediately normalize upon reaching a target weight, as the body needs time to rebuild fat stores and stabilize the hormonal environment. Psychological recovery is also important, since chronic stress and high cortisol levels can continue to suppress the GnRH signal even after initial weight gain. Long-term follow-up studies suggest that for those who achieve sustained weight restoration, the rates of pregnancy and childbirth are often similar to those of the general population. The reproductive system generally recovers its function once the energy balance is restored.
Pregnancy Risks Following Anorexia
While fertility is often restored after recovery, conception during active illness or shortly after stabilization can carry risks for both the mother and the developing fetus. Women who become pregnant while still underweight face increased chances of obstetric complications due to ongoing nutritional deficiencies. Specific risks include an increased likelihood of miscarriage and preterm birth. Infants born to mothers with active or recent AN are more likely to have a low birth weight and be small for their gestational age. For a healthy pregnancy, it is recommended that a woman establish a stable, healthy weight for several months before attempting conception.