If you have a luteal phase that is shorter than 12 days, you may have a difficult time getting, or staying pregnant. If your luteal phase is short a fertilized egg may not have time to implant itself in the uterine lining, to start a pregnancy, before your progesterone level drops and your period begins.
Not to worry though! There are many ways to lengthen your luteal phase. A good place to start is to make sure you have a healthy diet, with lots of whole foods, and healthy fats. Avocado oil, hemp seed oil, fish oil, and organic butter are examples of these.
Once your diet is in order, and if your luteal phases are still in the 9 to 11 day range, you may want to consult with an herbalist or acupuncturist, both of these modalities have been shown to help correct cycle irregularities.
If you're looking to go a more medical route, talk to your doctor about progesterone supplementation after ovulation.