Pregnancy quiz: Can you deliver on the science of growing babies?

Two pregnant people sitting and writing — Pregnancy starts on the first day of the last menstrual period before conception.

(Image credit: JGI/Jamie Grill via Getty images)

As placental mammals, humans give birth to live young. Pregnancy begins on the first day of the last menstrual period, roughly two weeks before conception.

A human pregnancy consists of three trimesters and generally lasts around nine months. But how much do you know about how babies develop? For example, did you know some cell types appear only during pregnancy, or that hair usually grows thicker and lusher during pregnancy due to hormones, but that this extra hair falls out months later after giving birth?

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Sophie is a U.K.-based staff writer at Live Science. She covers a wide range of topics, having previously reported on research spanning from bonobo communication to the first water in the universe. Her work has also appeared in outlets including New Scientist, The Observer and BBC Wildlife, and she was shortlisted for the Association of British Science Writers' 2025 "Newcomer of the Year" award for her freelance work at New Scientist. Before becoming a science journalist, she completed a doctorate in evolutionary anthropology from the University of Oxford, where she spent four years looking at why some chimps are better at using tools than others.