If parents don't want to use unreliable methods, they have the option of waiting for the regular mid-pregnancy ultrasound, usually performed between 18-20 weeks gestation. Though some families are offered other tests earlier in pregnancy that can identify the boys from the girls. These tests, because they pose risks to the pregnancy, are usually done only in the case of parents who have reason to worry about genetic problems. These tests are the chorionic villus sampling (CVS) test and the amniocentesis (amnio).
The Ramzi's Method is original research done by Dr. Saad Ramzi Ismail. In this multi-center prospective cohort study, more than 5,000 fetuses were scanned for placental location and gender. These scans were done over a ten year period in Canada. The same sonographer did all of the exams. In the first trimester, six weeks gestation, 22% of the mothers had transvaginal ultrasounds performed. 78% of the mothers chose to have a regular transabdominal ultrasound done. They measured both gestational age as well as where the placenta was located. The mothers returned between weeks 18-20 and were rescanned using the abdominal ultrasound. 99% of the fetal genders were confirmed at this point and 100% of the results were confirmed at birth. This study did not include twins, ectopic pregnancies, and other complications.
In using this data, Dr. Ramzi Ismail concluded that at six weeks gestation, 97.2% of the male fetuses had a placenta or chorionic villi on the right side of the uterus. When it came to female fetuses, there were 97.5% of the chorionic villi or placenta on the left side of the uterus.
This is amazingly accurate and has nothing to do with actual visualization of the sex organs, which is impossible this early in pregnancy. Parents want to know the sex of their baby for many reasons, including to figure out how to manage a pregnancy when there may be certain sex linked diseases complicating it. Though the author encourages this to be used as a soft marker to be used between the physician and patient when earlier knowledge can help the team with decision making.
The biggest advantage here is that the use of 2D ultrasound does not pose the risks that other methods do to the pregnancy. It can also easily be incorporated into the first trimester screenings and the results are immediately available. This can also prevent the waiting times that can cause much anxiety for families.
Though this is not widely used anywhere currently, parents wishing to know the sex of their baby may be trying to figure this out any way. If you have an early ultrasound and are not trained, you may misinterpret the results, even if you can clearly see the screen. You would be better off asking the person doing the ultrasound which side the placenta is on, than trying to guess yourself.
It would be wise not to make decisions that are irreparable because of this knowledge. I'm not even sure if I'd paint a nursery with this answer. (Though I hate to paint, so keep that in mind!) My best advice is to make sure that both you and your partner want to know and know what you'd do with the information before finding out. Dr. Ramzi Ismail also recommends that both parents be told at the same time.
Ramzi Ismail, Saad. "The Relationship Between Placental Location and Fetal Gender (Ramzi’s Method)." Web.