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Day 127 of 300 · Week 17

Eighteen weeks: sleep at 4 to 5 months

Last reviewed · 3 min read · 12 sources · Plain-text version

Eighteen weeks: how much sleep babies this age need, why 'sleeping through' varies so much from baby to baby, and the short bedtime routine with the best evidence behind it.

A white father in a dim nursery lowers his eighteen-week-old onto their back in a bare crib, the baby in a sleep sack with eyes half open, a small lamp glowing and a board book on the chair.

Eighteen weeks. Sleep is the question everyone asks you about now, so here is what's known.

Heart

Babies 4 to 12 months need 12 to 16 hours of sleep in 24 hours, naps included (Paruthi et al., 2016); the AAP supports that guidance and notes that some babies need a bit more or less (AAP). Regular sleep cycles arrive at about 4 months (AAP). What "sleeping through the night" means is the part that varies.

Head

It varies a lot. In a study of 75 New Zealand babies, 21 still weren't sleeping from 10 p.m. to 6 a.m. at 12 months (Henderson et al., 2010). In a Canadian study of 388 babies, 27.9% to 57.0% of 6- and 12-month-olds didn't sleep 6 to 8 hours straight, and that wasn't linked to their development (Pennestri et al., 2018). Night waking at this age is common and normal, whether or not anyone calls it a "4-month sleep regression."

Body

The routine is what the evidence likes. A survey of more than 10,000 mothers linked consistent bedtime routines with better sleep, though it can't prove cause (Mindell et al., 2015), and in a trial of 405 families of babies and toddlers, a consistent bedtime routine improved sleep and mothers' mood within weeks (Mindell et al., 2009). Keep it short and the same each night, and don't put your baby to bed with a bottle (AAP). A regular wake time and active days help too (AAP).

Try today

  1. The mother on the nursery chair with the baby on her lap, wiping the baby's gums with a soft damp cloth wrapped around her finger, a board book open on the arm of the chair.

    Brush, book, bed

    Time: 10 to 15 minutes at the same time each night · Brush, book, bed in the guide

    1. Wipe your baby's gums with a soft, damp cloth (or brush a first tooth with a rice-grain smear of fluoride toothpaste).

    2. Read one short book in dim light.

    3. Lay your baby on their back in their own sleep space at a regular time (AAP).

    Make it work:

    The order is the routine. Same three steps, same lamp, same song if you have one, every night, including the bad ones.

Watch for

  • Normal

    waking at night; in one study, 27.9% to 57.0% of 6- and 12-month-olds didn't sleep 6 to 8 hours straight (Pennestri et al., 2018).

    Call your pediatrician within 24 hours

    about any fever at 3 to 6 months, and sooner if your baby seems very sick (AAP).

  • Normal

    falling asleep on the breast or bottle. Never put a baby to bed with a bottle (AAP).

    Go to the ER now

    if your baby is hard to wake or isn't alert when awake (AAP).

  • Normal

    a baby at the edges of the 12-to-16-hour range; some need a bit more or less (AAP).

    Call 911

    if your baby is struggling for each breath or has bluish lips or face (AAP).

For you

Both parents at the kitchen table after dark, a notepad between them with a short list, mugs of tea, the baby monitor showing the baby asleep on their back in the bare crib.

Sleep training is optional. Nobody has to do it, and tomorrow's note is only for those thinking about it. If that's you, here are the questions to bring to the pediatrician: which approach, gradual or checking without soothing; when, since pediatricians generally give the okay at 3 or 4 months (Lurie Children's); what happens to night feeds; and how every safe sleep rule stays in place, back to sleep, a bare crib, and room-sharing for at least the first 6 months (Moon, AAP). Write the four questions on one page tonight.

If you're the partner: this is a two-adult decision. The one who does the 2 a.m. feed doesn't get to decide alone, and neither does the one who doesn't.

Sources

This guide is general education that summarizes published research and guidance from groups like the American Academy of Pediatrics, the CDC, and the WHO. It isn’t medical advice, and every child develops on their own timeline. Your pediatrician knows your child; if something feels wrong, call them. In an emergency, call 911.

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