Recently, two advanced trainee paediatricians of my acquaintance have become first-time mothers in their early 30s and have felt almost overwhelmed by having a demanding newborn baby. These highly capable young women are used to nocturnal sleep deprivation, although when you are on call you can look forward to some rest when your shift ends. But they both described how the lack of sleep drained them of energy and confidence. They felt to blame for their baby’s crying, even though, at an intellectual level they had read and were well aware that many babies cry a lot during their first few weeks of life. They knew of the fourth trimester, a term coined by US paediatrician Harvey Karp referring to the 3 months that babies cry inconsolably every evening.1 The concept of the fourth trimester is that human babies are born less mature than other animals and may need nurturing as if they were in utero (Fig. 1). The mothers tried swaddling and shushing to soothe their babies as suggested in the world according to Karp. And still the babies cried, and the young mothers felt to blame and struggled to cope.