Final answer:
The most reliable way to confirm the sex of a baby is through examining sex chromosomes with genetic testing procedures.
Step-by-step explanation:
The most reliable way to confirm sex is by examining the sex chromosomes, which are a special pair known as sex chromosomes. These chromosomes, X and Y, determine the gender of a baby. A typical female chromosome configuration is XX, whereas a typical male is XY. It is possible to assess these chromosomes through genetic testing procedures, such as karyotyping or noninvasive prenatal testing (NIPT).
Techniques like fertility awareness methods are used for estimating fertile days of the menstrual cycle to prevent pregnancy, but they do not have any impact on determining the sex of a baby. These methods often require the use of a home ovulation predictor kit to track ovulation, but this is for fertility purposes and not for sex determination.