MayoClinic.com notes these developmental milestones:
Growth is rapid this week. Just four weeks after conception, your baby is about 1/8 of an inch long. The neural tube along your baby's back is now closed, and your baby's heart is beating with a regular rhythm.
Basic facial features will begin to appear, including an opening for the mouth and passageways that will make up the inner ear. The digestive and respiratory systems begin to form as well.
Small blocks of tissue that will form your baby's connective tissue, ribs and muscles are developing along your baby's midline. Small buds will soon grow into arms and legs.
The Visible Embryo notes the following:
SIZE: 9.0 - 11.0 mm
TIME PERIOD: 37 - 42 days post-ovulation
Head and Neck
Brain is well marked by its cerebral hemispheres. The hindbrain, which is responsible for heart regulation, breathing and muscle movements, begins to develop.
Future lower jaw, the first part of face to be established, is now visible while future upper jaw is present, but not demarcated.
Mesenchymal cells originating in the primitive streak, the neural crest and the prechordal plate, continue to form the skull and the face.
External retina pigment is visible and the lens pit has grown into a D shape. Nasal pits are still two separate plates, but they rotate to face ventrally as head widens.
Primary cardiac tube separates into aortic and pulmonary channels and the ventricular pouches deepen and enlarge, forming a common wall with their myocardial shells. ....
Abdomen and Pelvic Regions
The mesentery, which attaches the intestines to the rear abdominal wall, holds them in position and supplies them with blood, nerves and lymphatics, is now clearly defined. Ureter, the tube that will convey urine from the kidney to the bladder, continues to lengthen. Proliferation of the coelomic epithelium indicates the gonadal primordium.
Hand region of upper limb bud differentiates further to form a central carpal part and a digital plate. The thigh (rostrolateral part), leg (the caudomedial part) and foot areas can be distinguished in the lower limb buds.
This embryo, taken from an ectopic pregnancy, is the correct size, so I'm assuming it's developmentally similar:
This photo of an opened oviduct with an ectopic pregnancy features a spectacularly well preserved 10-millimeter embryo. ....
Even an embryo this tiny shows very distinct anatomic features, including tail, limb buds, heart (which actually protrudes from the chest), eye cups, cornea/lens, brain, and prominent segmentation into somites. The gestational sac is surrounded by a myriad of chorionic villi resembling elongate party balloons. This embryo is about five weeks old (or seven weeks in the biologically misleading but eminently practical dating system used in obstetrics).
So, there the embryo is, with its developing brain, beating heart, and intestines in place. How does one go about killing it?
The standard method is a suction abortion. With an embryo this small, some practitioners (especially adherents of "self-help" home abortions) use a manual suction device consisting of a large syringe and a narrow tube. Others use the suction machine, with a Karman canula, invented by prochoice icon Harvey Karman.
Here is a chipper ad for these evidently delightful abortions. (Note screen capture, right)
Chemical or "medical abortions" are becoming more popular, and in some cases plugged as "home abortions". One drug is used to kill the embryo -- typically methotrexate, a powerful anti-arthritis drug, also used to treat cancer, that attacks the cells in the body that are dividing most rapidly. A second drug -- Cytotec or another prostaglandin -- us then used to cause uterine contractions to ensure that the dead embryo is expelled.
I couldn't find any "after" photos that early, but did find the following images at the Center for Bioethical Reform of 7-week embryos post-abortion:
Now, for women's stories: