Pregnancy - identifying fertile days

Definition

Fertile days are the days a woman is most likely to get pregnant.

Infertility is a related topic.

Alternative Names

Basal body temperature; Infertility - fertile days

Information

When trying to become pregnant, many couples plan intercourse between days 11 to 14 of the woman's 28-day cycle. This is when ovulation occurs.

It is hard to know exactly when ovulation will happen. Health care providers recommend that couples who are trying to have a baby have sex between days 7 and 20 of a woman's menstrual cycle. Day 1 is the first day of menstrual bleeding. In order to become pregnant, having sex every other day or every third day works just as well as having sex every day.

  • Sperm can live inside a woman's body for less than 5 days.
  • A released egg lives for less than 24 hours.
  • The highest pregnancy rates have been reported when the egg and sperm join together within 4 to 6 hours of ovulation.

If you have an irregular menstrual cycle, an ovulation predictor kit can help you know when you are ovulating. These kits check for luteinizing hormone (LH) in the urine. You can buy them without a prescription at most drug stores.

There are various other methods to help detect when you are most likely to be able to conceive a baby.

Note: Some lubricants can interfere with conception. If you are trying to get pregnant, you should avoid all douches and lubricants (including saliva), except those specifically designed to not interfere with fertility (such as Pre-seed). Lubricants should never be used as a method of birth control.

EVALUATING YOUR CERVICAL FLUID

Cervical fluid protects the sperm and helps it move toward the uterus and fallopian tubes. Cervical fluid changes occur when the woman's body is getting ready to release an egg. There are clear differences in how it looks and feels during the woman's monthly menstrual cycle.

  • No cervical fluid is present during the menstrual period.
  • After the period is over, the vagina is dry and no cervical fluid is present.
  • Fluid then turns to a sticky/rubbery fluid.
  • The fluid becomes very wet/creamy/white which indicates FERTILE.
  • The fluid becomes slippery, stretchy, and clear like an egg white, which means VERY FERTILE.
  • After ovulation, the vagina becomes dry again (no cervical fluid). The cervical mucus may become more like thick bubble gum.

You can use your fingers to see how your cervical fluid feels.

  • Find the fluid inside the lower end of the vagina.
  • Tap your thumb and first finger together -- if the fluid stretches while you spread your thumb and finger apart, this could mean ovulation is near.

TAKING YOUR BASAL BODY TEMPERATURE

After you ovulate, your body temperature will rise and stay at a higher level for the rest of your ovulation cycle. At the end of your cycle, it falls again. The difference between the 2 phases is most often less than 1 degree.

  • You can use a special thermometer to take your temperature in the morning before you get out of bed.
  • Use a glass basal thermometer or a digital thermometer that is accurate to the tenth of a degree.
  • Keep the thermometer in your mouth for 5 minutes or until it signals you that it is done. Try not to move too much, as activity can raise your body temperature slightly.

If your temperature is between 2 marks, record the lower number. Try to take your temperature at the same time every day, if possible.

Create a chart and write down your temperature every day. If you look at a complete cycle, you will probably notice a point at which the temperatures become higher than in the first part of your cycle. The rise is about 0.2 degrees or more above the previous 6 days.

Temperature is a useful indicator of fertility. After checking for several cycles, you may be able to see a pattern and identify your most fertile days.

References

Catherino WH. Reproductive endocrinology and infertility. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 218.

Ellert W. Fertility awareness-based methods of contraception (natural family planning). In: Fowler GC, ed. Pfenninger and Fowler's Procedures for Primary Care. 4th ed. Philadelphia, PA: Elsevier; 2020:chap 117.

Lobo RA. Infertility: etiology, diagnostic evaluation, management, prognosis. In: Gershenson DM, Lentz GM, Valea FA, Lobo RA, eds. Comprehensive Gynecology. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 40.

Rivlin K, Davis AR. Contraception and abortion. In: Gershenson DM, Lentz GM, Valea FA, Lobo RA, eds. Comprehensive Gynecology. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 13.

Review Date: 3/31/2024
Reviewed By: LaQuita Martinez, MD, Department of Obstetrics and Gynecology, Emory Johns Creek Hospital, Alpharetta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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