18 Days: The heart is forming.

20 Days: Foundations of the brain, spinal cord and the entire nervous system are laid.

24 Days: The heart begins to pulsate.

28 Days: Forty pairs of muscles are developing along the future spine. Arms and legs are budding.

30 Days: From one to millions of cells, the embryo has grown 10,000 times and is 6-7mm (1/4 in.) long. The brain has human proportions. Blood flows in veins (but the child’s bloodstream remains separate from the mother’s throughout pregnancy).

35 Days (5 weeks): The pituitary gland is forming in the middle of the brain. Mouth, ears and nose are taking shape.

40 Days: The heart’s energy output is already 20 percent of an adult’s.

42 Days (6 weeks): The child’s skeleton is formed (in cartilage, not yet bone). The brain co-ordinates movements of muscles and organs. Reflex responses have begun. In boys, the penis is forming. (And the mother misses her second period.)

43 Days: Brainwaves can be recorded.

45 Days: Spontaneous movements have begun. Buds of milk teeth have appeared.

7 weeks: Lips are sensitive to touch. Ears may already resemble a family pattern.

8 weeks: The child is a well-proportioned, small-scale baby measuring just 3cm sitting up and weighing a gram. Every organ is present. The heart beats sturdily. The stomach produces digestive juices. The liver manufactures blood cells. The kidneys begin to function. Taste buds are forming.

8 1/2 weeks: Fingerprints are being engraved. Eyelids and palms of the hand are sensitive to touch. The child feels pain.

9 weeks: The child will bend his or her fingers around an object placed in the palm. Thumb sucking occurs. Fingernails are forming.

10 weeks: The entire body is sensitive to touch (except for the sides, back and top of head). The child squints, swallows, puckers up his or her brows and frowns.

11 weeks: He or she can make complex facial expressions – even smile. The baby urinates.

12 weeks: Activity has become vigorous and behaviours shows distinct individuality. The child can kick legs, turn feet, curl and fan toes, make a fist, move a thumb, bend a wrist, turn the head, open the mouth and press lips tightly together. Breathing is practised.

13 weeks: Facial expressions already resemble those of the parents. Movements are graceful and flowing. Reflexes are vigorous. Vocal chords are formed (but in the absence of air the baby cannot cry aloud). Sex organs are apparent and primitive sperm or egg cells are present.

4 months: The child can use hands to grasp, swims and turns somersaults.

4-5 months: Mother first feels her baby’s movements.

5 months: Sleeping habits appear. To sleep, the child settles into a favourite position. A loud noise, such as a door slamming, will provoke activity. The child also responds to sound in frequencies too high or low for adults to hear. Many babies born at this age are surviving with good medical care.

6 months: Fine baby hair grows on eyebrows and head. A fringe of eyelashes appears. Most of the skeleton has hardened. Weight is about 640g and height about 23cm. Babies born at this age have been known to survive.

7 months: Eyelids open and close, and eyes look around. Hands grip strongly. Mother’s voice can be heard and recognized. The baby begins to accumulate some fat.  Permanent eye teeth are present.

8 months: Weight increases by 1kg and the baby’s quarters begin to get cramped.

8 to 9 months: Labour begins (triggered by the child) and birth occurs, usually 255-275 days after conception. Of the 45 generations of cell divisions between conception and adulthood, 41 have taken place. The remaining four will occur during the rest of childhood and adolescence.

The milestones listed above have been documented by scientific research. Slight variations, of hours or days, may exist and future research using more sensitive methods may show that some of these milestones occur earlier than is now realised.