It is possible to become pregnant during perimenopause, the natural transition phase leading up to the end of a woman’s reproductive years. While fertility declines, the ovaries still occasionally release a viable egg, meaning conception can occur unexpectedly. Perimenopause involves hormonal shifts signaling the body is nearing menopause, the point at which pregnancy is no longer possible. Women wishing to avoid pregnancy must continue to use effective contraception throughout this transitional period.
Defining the Perimenopause Transition
Perimenopause, often called the menopausal transition, is the period when the body naturally prepares for the complete cessation of menstrual cycles. This phase typically begins in a woman’s 40s, though it can start earlier, and can last anywhere from a few months to over a decade. The average age for natural menopause is 51, and perimenopause spans the years leading up to that final menstrual period.
The defining characteristic of this transition is the fluctuation of reproductive hormones, particularly estrogen and progesterone. A decrease in the hormone inhibin causes the pituitary gland to release more follicle-stimulating hormone (FSH) to prompt the ovaries to work harder. This hormonal instability leads to common symptoms signaling the start of perimenopause, such as irregular menstrual periods, hot flashes, and mood changes.
Fertility and Irregular Ovulation
The possibility of pregnancy during perimenopause hinges on the fact that ovulation has not stopped entirely, even if it has become erratic. Fluctuating hormone levels cause menstrual cycles to become unpredictable; periods may be shorter, longer, lighter, or heavier, and can skip months entirely. Despite this irregularity, the ovaries are still capable of releasing an egg, meaning conception remains possible.
The primary biological mechanism behind reduced fertility is a decline in the quantity and quality of the remaining eggs, known as the ovarian reserve. Released eggs are more likely to have chromosomal abnormalities, which increases the risk of miscarriage. While many cycles may be anovulatory (meaning no egg is released), some cycles will still result in ovulation. This occasional release of an egg allows pregnancy to occur in late perimenopause, even when periods are infrequent.
Contraception Considerations
Because sporadic ovulation still occurs during perimenopause, continued use of birth control is necessary for anyone who does not wish to become pregnant. The choice of contraception should be discussed with a healthcare provider, considering a woman’s age, health status, and perimenopausal symptoms. Some hormonal contraceptives, such as low-dose combined hormonal pills or hormonal intrauterine devices (IUDs), offer the dual benefit of pregnancy prevention and management of symptoms like heavy or irregular bleeding.
Progestin-only methods, including implants, injections, and hormonal IUDs, are suitable during this phase because they avoid risks associated with estrogen, which can increase with age and pre-existing conditions. Long-acting reversible contraceptives (LARCs), such as the copper IUD or hormonal IUDs, are highly effective and convenient, providing years of protection without needing daily attention. For women with certain health risks, non-hormonal barrier methods like condoms are a safe option and offer protection against sexually transmitted infections.
Confirming the End of Fertility
The end of the perimenopausal transition is marked by the milestone of menopause. Menopause is a single point in time, defined retrospectively as having occurred after a woman has gone 12 consecutive months without a menstrual period. This diagnostic criterion must be met in the absence of other causes, such as certain medications or health conditions.
Once this 12-month period of amenorrhea is confirmed, a woman is considered postmenopausal, and the risk of natural conception is zero. This clinical definition signals that contraceptive measures are no longer required. For women using hormonal birth control that suppresses periods, a blood test to check follicle-stimulating hormone (FSH) levels can help determine if menopause has been reached.