How reliable is the estimation if after an ultrasound at 18 weeks they could not tell the sex of the baby but offered a guess?

I think he guessed and has a 50/50 chance of being correct. You could buy pink clothes if you see something irresistible but don't open them and do keep the receipts so you can exchange them if necessary. You cannot always see the penis in a boy or the vulva in a girl if the baby keeps its legs together so you cannot always tell the sex. Wait until your next ultrasound to see if your baby is being a little more cooperative don't start buying pink or blue things yet stick to some neutral stuff for now if you just can't help yourself my baby had his legs open all the time I knew I was having a boy at 14 weeks but my best friend had to wait until she was 26 weeks to find ou t she was having a girl so it just depends on your baby good luck God Bless and Congratulations on your up and coming new addition!!!