Haha mommy, ang ultrasound readings ay medyo tricky talaga lalo na kung maliit pa ang baby or kung hindi clear ang angle, a few of us tried to guess based sa nub theory tapos biglang boy pala or vice versa! Best bet talaga is to ask your OB directly kung confident siya sa result, kasi sila ang trained to read it properly, and some clinics pwede pang mag-repeat ultrasound if uncertain pa, especially around 18-20 weeks when mas clear na talaga.