Most women will get pregnant within six months of trying if they have no fertility problems and have intercourse during their most fertile days. Some women will conceive in the first cycle, while others will take longer than six months. Several factors can influence the normal average time to conception.
Pregnancy Rates Over Time
Researchers reported a study of a group of women using natural fertility planning methods to time intercourse to try to conceive in Human Reproduction in 2003. The study looked at how many months it took these women to conceive without treatment.
The researchers found by six months most of the women had conceived, and a further 10 percent got pregnant over the next six months. Specific total percentage of women who were pregnant by certain months of trying to conceive were as follows:
- By one month: 42 percent
- By three months: 75 percent
- By six months: 88 percent
- By one year: 98 percent
Monthly Chance of Pregnancy
With timed intercourse if you are less than age 35, you have about a 30 to 35 percent chance of getting pregnant each menstrual cycle. This is based on the above cited study and research reviewed in 2005 in another article in Human Reproduction by the same authors. In addition:
- Your monthly chance of getting pregnant is highest during the first three cycles of unprotected sex and decreases after that.
- If you are not pregnant after one year of consistently trying, you still have about a 50 percent chance of conceiving during the following year.
- Your chance is lower after 36 months and approaches zero after 48 months of no conception despite timed intercourse.
Your chance of pregnancy each cycle decreases as you get older.
Factors That Affect Time to Conception
If your fertility is normal, whether you get pregnant in the first month of trying or take longer is first a matter of chance - a "throw of the dice." The main factors that underlie the average chance of getting pregnant each month include the normal variation in:
- Timing of ovulation and intercourse each cycle
- The quality of the egg each cycle
Second, several other factors that affect your ability to get pregnant can modify this background chance and increase your time to conception.
Ovulation and Timing of Intercourse
Optimum timing of intercourse to match ovulation is a critical factor in your chance of getting pregnant each cycle. If you are not tracking your ovulation and timing intercourse around that day, it can take you longer to conceive. The following information can help you with timing and improve your chance of pregnancy each cycle:
- You have a six day fertile window around ovulation during which you can conceive if you have intercourse.
- Your most fertile of these six days are the two days before and the day you ovulate - especially on the day before you ovulate.
- Tracking your signs of fertility such as cervical mucus changes or use of ovulation (LH) predictor kits can help you with this timing.
- You can also use a fertility calculator to estimate your day of ovulation.
It takes longer to conceive with age because of a decrease in fertility with aging in women and men. For women, a review of the literature published in 2011 in the Journal of Obstetrics and Gynaecology Canada indicates:
- The decrease in the likelihood of pregnancy each cycle becomes significant after age 35.
- The decline is due to the aging of the ovaries and therefore fewer and aging eggs and irregular ovulation.
Men over age 50 have a significant decrease in fertility capacity compared to men less than 30 years old, according to a review of studies published in 2001 in Fertility and Sterility. This is caused by a decline in sperm quality with age.
Problems with either the female or male reproductive systems interfere with conception ability and lengthen the time it takes to conceive. The Centers for Disease Control and Prevention reviews the following infertility factors:
- Tubal damage caused by sexually transmitted diseases, endometriosis, appendicitis, or abdominal surgery
- Uterine factors, such as fibroids, polyps that distort the cavity of the uterus and disturb implantation of the early pregnancy
- Male factors that cause abnormal sperm production, low sperm count, or poor sperm quality
Disturbance of ovulation is the easiest fertility problem to treat and the highest pregnancy rate after fertility treatment.
Health and Lifestyle Factors
Health and lifestyle factors can interfere with egg development, ovulation and egg quality, and sperm production and quality, and therefore fertility. These factors can increase the number of cycles it takes to conceive.
According to guidelines published in the journal Fertility and Sterility in 2013, the following health and lifestyle factors can affect fertility:
- Toxins such as solvents and mercury ingestion from eating a lot of seafood
Chronic medical illnesses, such as liver, kidney and heart disease, diabetes, cancer, thyroid, and autoimmune diseases can also play similar roles.
Medications Can Have an Impact
If you are not pregnant after six cycles of trying, consider the medicines you are taking and discuss them with your doctor. After stopping some types of hormonal contraceptives, some women might not return to regular ovulation for several months, thus taking longer to get pregnant. These include oral contraceptive pills, DepoProvera, and contraceptive implants.
In addition, prolonged use of some prescription, over-the-counter, and herbal medicines have the potential to affect ovulation in women and sperm production in men. This includes prolonged use of prescription and illegal steroids
First Versus Future Pregnancies
It might take you a shorter or longer time to conceive after your first pregnancy by a throw of the dice of chance. Having your first baby is a confirmation of your fertility, but it doesn't predict the journey to your second pregnancy and others.
Factors that can make it harder and lengthen the time to conceive your next baby compared to your first include:
- Post-partum complications, such as uterine or tubal infection
- Gynecologic and hormonal problems after delivery
- You could develop any of the fertility factors or medical problems described in the sections above
When to Seek a Fertility Evaluation
Standard recommendation is, if you are younger than age 35, you should consult your doctor for a fertility evaluation if you are not pregnant after one year of unprotected intercourse. If you are older than 35, see your doctor after six months of trying.
Consider Seeking Help After Six Months at Any Age
Most women will conceive within six months of trying. Therefore, even if you are younger than 35 years, if you are concerned, consider consulting your gynecologist or a fertility specialist if you are not pregnant after six months.
This advice is based on the data from the research cited in the first section above, "Pregnancy Rates Over Time," and the 2013 Fertility and Sterility guidelines in the "Health and Lifestyle Factors" subsection. At any age, seek help soon if you have a known fertility issue or a medical problem that can interfere with your fertility.