The number that matters: 21 days

The NHS is unambiguous: “you can get pregnant 3 weeks after the birth of a baby, including if you're breastfeeding and your periods haven't started again”, and “you need to use contraception every time you have sex after giving birth unless you want to get pregnant again.” The practical deadline it gives is to start contraception within 21 days of the birth.

ACOG explains the biology behind it. If you are not breastfeeding, “ovulation may occur within a few weeks of childbirth”. If you are breastfeeding it may be delayed, “but it usually returns by about 6 months.” Crucially: “ovulation usually occurs 2 weeks before your menstrual period starts. This means that you can get pregnant even if you have not yet had a period.” Waiting for a period is waiting for evidence that arrives two weeks too late.

ACOG also notes that “many experts recommend waiting at least 18 months between pregnancies before having another baby”, and Ireland's HSE advises waiting at least 6 months after a caesarean before trying again.

What you can start immediately

The NHS lists methods you can begin straight after the birth, including while breastfeeding:

The contraceptive implant
The contraceptive injection
The progestogen-only pill
Condoms and internal (female) condoms
An IUD (copper coil) or IUS (hormonal coil)

There is a timing catch with the coil. The NHS: “if an IUD or IUS is not fitted within 48 hours of giving birth, it's recommended to wait until 4 weeks after the birth.” ACOG says the same — IUDs “can be inserted right after a vaginal or cesarean birth or at your first postpartum health care visit” — but adds a trade-off worth knowing: an IUD comes out of the uterus in about 5 in 100 users in the first year, and “it is more common for the IUD to come out of the uterus when it is inserted right after delivery.”

ACOG confirms the implant and the injection can also be given immediately after a vaginal or caesarean birth.

What has to wait, and why

Combined methods: pill, patch and ring

These contain oestrogen, and the postnatal period already carries a raised risk of blood clots. The NHS: if you are not breastfeeding and a healthcare professional has checked you have no risk factors for a blood clot, you can start the combined pill, vaginal ring or contraceptive patch 3 weeks after the birth. If you are breastfeeding, “you'll usually be advised to wait until at least 6 weeks after the birth”.

ACOG's version: “during the postpartum period, there is a higher risk of developing blood clots in veins located deep in the body… Combined hormonal methods increase the risk of DVT even further. If you have no additional risk factors for DVT and you are not breastfeeding, you can start using these methods 3 weeks after childbirth.” On milk supply, ACOG says there is “a very small risk that the estrogen in these methods can affect your milk supply”, and to avoid them for the first 4 to 6 weeks of breastfeeding until feeding is established.

Diaphragm or cap

The NHS: you can usually start using a diaphragm or cap around 6 weeks after the birth — and if you used one before, “see a doctor or nurse at a contraception clinic to make sure it still fits correctly. You may need a new size.” ACOG makes the blunter point that “the sponge and cervical cap are much less effective after you give birth.”

Breastfeeding as contraception: the actual conditions

The lactational amenorrhoea method (LAM) is real, and it is conditional. The NHS says you are unlikely to have periods if you breastfeed exclusively and your baby is under 6 months old, but it lists the circumstances in which you must start another method:

Your baby is more than 6 months old
You give them anything apart from breast milk — including a dummy, formula or solid foods
Your periods start again, “even light spotting counts”
You stop night feeding
You start to breastfeed less often, or there are longer intervals between feeds, day and night

The NHS also notes that “the effect of expressing breast milk on LAM isn't known, but it may make it less effective” — which matters for anyone returning to work and pumping.

On the return of periods more generally, the NHS says that if you bottle feed, or combine bottle and breastfeeding, your first period could start as soon as 5 to 6 weeks after the birth. The HSE says that if you are breastfeeding your period may not return for at least 6 months, and that if you breastfeed and bottle feed it usually returns within 2 months.

Choosing before you need it

ACOG's advice is to decide during pregnancy: “a good time to choose the birth control method you will use after pregnancy is while you are still pregnant… Some can be started even before you leave the hospital.” It also flags that the method you used before pregnancy may not be the right one now.

In the UK, your midwife will discuss contraception with you after the birth (NHS), and you can talk to a GP, health visitor or sexual health clinic at any time. NICE NG194 requires contraception to be discussed at postnatal contacts, including the GP assessment at 6 to 8 weeks, and points clinicians to the Faculty of Sexual & Reproductive Healthcare guideline on contraception after pregnancy.

When to call

Speak to a GP, midwife, health visitor or sexual health clinic if:

You are 21 days past the birth and have no method in place.
You had unprotected sex after day 21 and do not want another pregnancy — emergency contraception is time-sensitive.
You are breastfeeding and want a combined method: this needs a conversation about timing and milk supply (NHS, ACOG).
You have risk factors for blood clots, migraine with aura, high blood pressure, or a history of stroke, heart attack or DVT — ACOG lists these as reasons combined methods are not recommended.
You used a diaphragm or cap before and want to use it again — it needs refitting (NHS).

Contact your GP or midwife urgently if you develop pain or swelling in one calf, chest pain or breathlessness, which can indicate a clot. Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, or 111 in New Zealand) for chest pain or severe breathlessness.

Contraception After Birth