Both clinical and laboratory studies have shown that the last day of the slippery sensation is the most fertile time in the cycle. It is called the Peak of fertility because it is the day when sex is most likely to result in a pregnancy. Studies show that ovulation usually occurs within a day of the Peak. It is important to realise that the Peak isn't necessarily the day of most mucus. The slippery, lubricative sensation may last a day or two after the visible signs of mucus, which means you're still highly fertile – the sensation is the more valuable symptom.