We wanted to understand what was happening beyond “the baby is the size of a seed.” Pick a question below; unfamiliar terms are explained as they come up.
Back to our baby & family news ←Tap a question to open it.
It starts by making three layers. Each helps build different things, from skin and nerves to muscles and lungs. Then that flat sheet folds into the beginnings of a body.
Gastrulation is the name for making those starting layers.
Meet the three layers →See those first folds →Yes! It starts as a simple tube that can contract. The tube bends and develops into a more familiar heart over the following weeks.
Those first contractions happen before a scan can show us that tiny flicker.
Follow the heart’s beginnings →What happens next? →The head is proportionally large at this stage because the brain is growing rapidly.
The body’s proportions change as it grows.
And the hands and feet? →Take a look at 12 weeks →Our baby starts moving long before Lindsay can feel it. Nerves and muscles are beginning to work together.
What else are they practising? →Developmental milestones, with dates and explanations.
Choose an organ system to follow its development.
What may appear on a scan at different stages.
Open a question to learn more.
The early ball of cells becomes a fluid-filled blastocyst. The cells that will form the body then organise into an embryonic disc, and later fold into the familiar curved embryo. “Embryo” includes those early flat stages, too.
After roughly eight weeks of development following fertilisation, we call our baby a fetus. The basic body plan is there, with plenty of growing and developing still ahead. These names help us follow the story; development keeps moving through them rather than switching overnight.
Our celebrations follow the calendar, while the drawings and explanations show the changes around each stage. The heart getting started means the early heart tube beginning to contract, which comes before the flicker we may see on an ultrasound.
The embryo starts making three layers of cells. That reshuffle is called gastrulation. Each layer has a different part to play, and the cells begin sending signals that help decide what grows where.
The outer layer (ectoderm) helps make skin, the nervous system and parts of the eyes and ears. The middle layer (mesoderm) helps make muscles, bones, the heart, blood and kidneys. The inner layer (endoderm) helps make the linings of the gut and lungs, and parts of the liver and pancreas.
Not every organ comes from just one layer: many organs combine contributions from two or all three.
A neural plate folds inward; its edges approach one another and fuse into the neural tube. The front of that tube enlarges into early brain regions, while the rest develops into the spinal cord.
The tube typically finishes closing near day 28 after fertilization, although the process varies. This is the critical developmental window behind the recommendation to take folic acid before conception and early in pregnancy.
Closure begins near the middle and progresses toward both ends, more like fastening a zipper than rolling up one sheet from a single edge.
Cells in a primitive heart tube start contracting around days 22–23. It's an early pump, not a miniature four-chambered adult heart. Over the following weeks the tube loops and partitions, and valves develop.
First contractions and first detectable ultrasound cardiac activity are different milestones. Motion may be visible on transvaginal ultrasound around 6–7 weeks of gestational age, depending on equipment, dating, and the particular pregnancy.
The arms and legs appear as small buds, then broaden into hand and foot plates. Finger rays appear within the hands around days 42–44. The fingers separate over the ensuing weeks.
Meanwhile the lens, nasal pits, external ear contours, eyelids, and portions of the face take shape. The embryo's head is dramatically oversized compared with its body because the brain is developing so rapidly.
The head is doing a lot of growing while the arms and legs catch up.
The middle part of the developing intestine grows faster than the tummy has room for. For a while, some of it sits in the base of the umbilical cord. That normal detour has quite a name: physiological midgut herniation.
The intestine usually returns to the abdomen around 10 weeks after fertilization (about 12 weeks pregnant).
Early fetal kidneys begin producing urine during the late first trimester. Over time, urine contributes substantially to amniotic fluid. The developing fetus also makes tiny swallowing and limb movements.
Lindsay won't feel these early movements yet. The neural and muscular systems are starting to coordinate, but the movement is much too small to register through the abdominal wall.
At about 10 weeks pregnant, our baby gets a new name: fetus. The main body plan and beginnings of the major organs are in place. There’s still a lot of growing and refining ahead.
Separately, cell-free DNA screening (NIPT) can generally be performed starting at 10 gestational weeks, not 10 weeks after fertilization. It analyzes predominantly placental DNA fragments in maternal blood and screens for certain chromosomal conditions. It is not a diagnostic test.
The secondary palate progressively joins, early bone mineralization continues, and the groundwork for fingernails and tooth development becomes more apparent. Eyelids develop and temporarily fuse over the eyes.
The external genitalia differentiate over this period, but their appearance may still be too similar to distinguish reliably on ultrasound. Many visible developments will continue well beyond the first trimester.
Pregnancy weeks count from the first day of the last period, usually about two weeks before fertilization. So “7 weeks pregnant” means roughly five weeks of our baby growing.
Our calendar uses the projected due date of June 14, 2027.