I agree that coconut oil is one of the best carrier oils that can be used with essential oils. It has tiny moleules so it allows the (also) small essential oil molecules to penetrate through the skin.
I would be interested in the essential oil brand you use. Some essential oils are cut or adulterated and this means there is no way of knowing the exact ingredients in the oil. Check that the oil meets all the criteria for a top quality oil.
The following info should be on the bottle: botanical name of plant, part of plant used, able to identify the country or origin, method of extraction, therapeutic grade.
If this information is not on the bottle, how do you know that you have genuine and pure essential oil? You don't.
The second thing is mandarin is a citrus oil and citrus oils are photosensitive. If you go out in the sun (or any UV light) after application the oil reacts with the UV light and can damage the skin causing a red or brown rash.
I recently did this while applying oil while stopped at the lights in my car. I put the oil on my heart chakra and the sun was shinning in through the window. When I got to my destination I went to the bathroom and looked in the mirror and I had a red rash at the base of my beautiful v-neck top!
Check a good reference book for oils to avoid with pregnancy. My favourite book is Essential Oils Desk Reference It has safety data tables in the Appendix. Best of luck with the pregnancy. There are some fantastic blends for labour and child birth too!
Jen