Is it possible to see an ectopic pregnancy through ultrasound at 4 weeks?

No. At 4 weeks gestational age (2 weeks after the missed expected menstrual period) it would be extremely unlikely to positively identify an ectopic on ultrasound. Ectopic may be suspected based on 4-week ultrasound, but until 5 or better 6 weeks ega ultrasound should not be considered absolutely diagnostic.