6 weeks pregnant: what is happening this week

Six millimetres, and the shape of a pea - which means the embryo has roughly tripled in a week. Growth in the first trimester is proportionally faster than it will ever be again, which is worth knowing because it makes the next few weeks of size figures look implausible when they are simply true. Limb buds have appeared: four small projections that become arms and legs. The heart, brain, liver and the beginnings of the musculoskeletal system are all developing at once, the ears have started, and the skin covering it all is transparent. Meanwhile, morning sickness has become the week's dominant fact for a good proportion of people, and the name remains one of the worst in medicine. It arrives at any hour, it responds poorly to being reasoned with, and it can make the ordinary business of eating into an exercise in negotiation. The NHS has a page on it that is genuinely practical, and the thing worth flagging from that page is the boundary: sickness severe enough to prevent keeping fluids down is a different situation with a different name, and it is a reason to call rather than to wait it out.