Natural family planning: how well it really works and who should avoid it

Their second baby is seven months old, and her period has already come back twice. She doesn’t want to use hormones while she is still breastfeeding, so the couple decide to go back to their old method. He brings up the rule “seven before, eight after” that they used before they had children, and she installs an app that colors the supposedly safe days green.

This way of avoiding pregnancy relies on the fact that each cycle has only a few days when conception is possible. But knowing exactly where those days fall is not easy, especially soon after giving birth, while breastfeeding, and before the cycle has settled back into a steady rhythm.

Each cycle has about six days when conception is possible

Wilcox and colleagues (1995) followed 221 healthy women who were trying to conceive over 625 cycles, pinpointing the day of ovulation through hormones in the urine. All 192 conceptions happened after sex within a six-day window ending on the day of ovulation. With sex five days before ovulation, the chance of conceiving was about 10%; on the day of ovulation itself, about 33%.

Five of those six days come before the egg is released. The reason is that sperm can survive for several days in a woman’s reproductive tract. To avoid pregnancy by abstaining, you have to predict the day of ovulation in advance, and that day can shift from one cycle to the next.

Common ways of counting days

Calendar counting

The Standard Days Method asks you not to have unprotected sex from day 8 to day 19 of the cycle, with day 1 being the first day of your period. The trial by Arévalo and colleagues (2002) only included women with cycles of 26–32 days, so for shorter or longer cycles this formula has not been tested.

The “seven before, eight after” rule is usually understood to mean that the seven days before a period and the eight days counted from the first day of bleeding are safe, though people may count it slightly differently. Read that way, the eighth day already reaches the point where the Standard Days Method starts abstinence. With a short cycle, ovulation comes early, and the last days of “eight after” may already fall inside the six-day window. Anyone who counts the eight days from when the bleeding stops goes even further into it. As for “seven before”, it only works if you know for sure when your next period will start.

Watching cervical mucus

Close to ovulation, the mucus in the vagina usually increases and becomes clear, wet and slippery, and may stretch into strings; those days count as fertile. After ovulation the mucus decreases and becomes thicker and stickier. Mucus is easy to confuse with discharge from an infection, so it usually takes a few cycles of practice to read it.

Basal body temperature

Body temperature measured right after waking up rises slightly once ovulation has happened. Because the rise comes afterwards, temperature only tells you that the fertile days have passed, and it is usually used together with mucus. If you are trying to conceive, how to read your cycle and temperature chart is covered in our article on the menstrual cycle when trying to conceive.

Pregnancy rates in real-life use

The review by Peragallo Urrutia and colleagues (2018) pooled 53 studies, none of which reached high quality. In the moderate-quality studies, the number of pregnancies in the first year of typical, everyday use, per 100 women, was:

• Standard Days Method: from 11.2 to 14.1;
• Mucus tracking (the Billings method): from 10.5 to 33.6;
• Basal body temperature: from 9.0 to 9.8;
• Mucus combined with temperature: 13.2 for one variant, 1.8 with Sensiplan.

With perfect use, following every rule exactly, the numbers are much lower, such as 0.4 with Sensiplan and 1.1–3.4 with Billings. For the Standard Days Method alone, Arévalo and colleagues (2002) reported a probability of pregnancy after 13 cycles of 4.75% with correct use and nearly 12% with typical use. The guidelines of the French College of Gynecologists and Obstetricians also state that natural methods are generally less effective than modern contraception, and that users should be told about the chance of failure in advance (Hassoun, 2018).

Who should not rely on counting days

Counting days is hard to use safely when:

• Your cycles are irregular, with lengths that vary a lot from month to month;
• You have recently given birth and are breastfeeding. Breastfeeding only prevents pregnancy up to 98% of the time when all three conditions are met: the baby is under 6 months old, your period has not come back, and the baby is fully or almost fully breastfed day and night (Hassoun, 2018); if any one condition is missing, you need another method;
• Your cycles start getting shorter or erratic in the years around perimenopause;
• An unplanned pregnancy would seriously harm your health, for example if you are taking medicine that should be avoided during pregnancy;
• You and your partner have not yet agreed on abstaining or using condoms on the fertile days.

If your baby is seven months old and your period has come back, you are in the second group. Breastfeeding no longer counts as contraception at this point, and your cycle is not yet steady enough to count. After giving birth, the first ovulation can come even before the first period. So not having a period yet does not mean you cannot get pregnant. Natural methods also do not protect against sexually transmitted infections.

How the clinic can help

A consultation with Dr. Pham Tran Dan Tam (MD, Specialist Level I in Traditional Medicine) starts with your period calendar over the last few months, your births, breastfeeding, and whether you plan to have more children. If you would like an IUD or another modern method, the choice of which one will be discussed with an obstetrician-gynecologist. A cycle so erratic that it cannot be counted also needs its cause found, including conditions that need modern medical care such as PMOS (polycystic ovary syndrome). Before regulating your periods, the doctor needs to be sure you are not pregnant; if your period is late, take a pregnancy test before using any medicine, including herbal decoctions.

Worth keeping

• Mark the first day of each period on a calendar to see whether your cycle falls within 26–32 days;
• If you use day counting, abstain or use condoms from day 8 to day 19 of the cycle;
• If you are breastfeeding, recheck all three conditions (baby under 6 months, no period yet, fully breastfed) whenever anything changes;
• Bring your period calendar for the last few months when you go for contraception advice.

If you are weighing up contraception after giving birth, or aren’t sure your cycle is regular enough to count, come and see Dr. Pham Tran Dan Tam (MD, Specialist Level I in Traditional Medicine) to go over your period calendar together and choose the right approach.

References

1. Wilcox AJ, Weinberg CR, Baird DD (1995). Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med 333(23):1517-21. https://doi.org/10.1056/NEJM199512073332301;
2. Peragallo Urrutia R, Polis CB, Jensen ET, Greene ME, Kennedy E, Stanford JB (2018). Effectiveness of Fertility Awareness-Based Methods for Pregnancy Prevention: A Systematic Review. Obstet Gynecol 132(3):591-604. https://doi.org/10.1097/AOG.0000000000002784;
3. Arévalo M, Jennings V, Sinai I (2002). Efficacy of a new method of family planning: the Standard Days Method. Contraception 65(5):333-8. https://doi.org/10.1016/s0010-7824(02)00288-3;
4. Hassoun D (2018). [Natural Family Planning methods and Barrier: CNGOF Contraception Guidelines]. Gynecol Obstet Fertil Senol 46(12):873-882. https://doi.org/10.1016/j.gofs.2018.10.002.