At six weeks pregnant, the embryo measures roughly 5 to 9 millimeters, about the size of a pomegranate seed, and your body is unlikely to show any visible change on the outside. Most of what’s happening at this stage is invisible to everyone but an ultrasound machine. Here’s what’s actually going on, both inside the uterus and in your own body.
How Big the Embryo Is at 6 Weeks
Crown-rump length, the standard measurement from head to bottom, ranges from about 5 mm at the start of week six to 9 mm by the end of it. That’s smaller than a single blueberry. Growth is rapid at this point; the embryo roughly doubles in size over just a few days.
Despite being tiny, the embryo is going through a burst of structural development. Tiny buds that will become arms and legs are forming, and the earliest structures for the ears, eyes, and mouth are taking shape. The neural tube, which becomes the brain, spinal cord, and the rest of the central nervous system, closed during week five and is now developing further. The heart has started beating, though it may or may not be detectable on ultrasound depending on the exact day and the equipment used.
What a 6-Week Ultrasound Shows
If you have an early ultrasound at six weeks, it will almost always be transvaginal rather than abdominal, because the embryo is too small to pick up through the belly. On screen, you’ll typically see a dark, round gestational sac with a smaller circle inside it (the yolk sac, which nourishes the embryo before the placenta takes over). Alongside the yolk sac, a fetal pole, the very first visible form of the embryo, can usually be seen.
A heartbeat is sometimes visible as a tiny flicker on the screen, but not always. At exactly six weeks, the heart may have just started beating, so whether it shows up depends on timing down to the day. If no heartbeat is detected, your provider will typically schedule a follow-up scan a week or two later rather than drawing any conclusions from a single early scan.
For women with a history of recurrent miscarriage, research from the Miscarriage Association shows that reaching six weeks of pregnancy comes with a 78% chance of the pregnancy continuing. Once a heartbeat is confirmed at eight weeks, that number jumps to 98%, and by ten weeks it reaches 99.4%.
What Your Body Looks Like
You won’t have a visible bump at six weeks. Your uterus, normally about the size of a plum, has grown to roughly the size of an egg. That’s not enough to push your belly outward. The uterus doesn’t rise above the pubic bone until around 12 weeks, which is when most people start to show.
Some women notice their pants feel slightly tighter, but this is almost entirely due to bloating from the hormone progesterone slowing digestion, not actual uterine growth. Weight gain at this stage is minimal or nonexistent, and some people actually lose a pound or two from nausea.
Symptoms You’re Likely Feeling
Six weeks is when many early pregnancy symptoms hit their stride. The pregnancy hormone hCG, which drives a lot of these symptoms, is climbing fast. At six weeks, hCG levels typically range from 200 to 32,000 units per liter, a wide range that reflects normal variation between pregnancies.
Nausea is one of the hallmark symptoms at this stage. It usually begins between weeks four and six, and despite being called morning sickness, it can strike at any time of day. Some people feel queasy without ever vomiting, while others throw up multiple times a day. Both patterns are common.
Breast tenderness often starts around the same time, between four and six weeks. Your breasts may feel swollen, sore, or unusually sensitive to touch. This is driven by hormonal changes, particularly rising estrogen and progesterone, and tends to be one of the earliest noticeable physical signs of pregnancy.
Other common experiences at six weeks include fatigue that feels disproportionate to your activity level, frequent urination (your kidneys are already processing more blood volume), food aversions or cravings, and mood swings. Not everyone gets all of these, and some people have very few symptoms at six weeks while still having a perfectly healthy pregnancy.
Why Everyone’s Experience Varies
The wide range of hCG levels at this stage, from 200 to 32,000, helps explain why two people at the same point in pregnancy can feel completely different. Someone at the higher end of that range may have intense nausea and fatigue, while someone at the lower end might barely feel pregnant at all. Both situations are normal. hCG levels also don’t follow a fixed number for a given week; what matters more is that levels are rising appropriately over time rather than hitting a specific target.
Similarly, embryo size varies. A measurement of 5 mm and a measurement of 9 mm can both fall within week six depending on exact gestational age and individual growth patterns. Ultrasound dating at this stage is accurate to within a few days, which is why early scans are considered reliable for establishing a due date.