The study, carried out by the Guttmacher Institute in New York in collaboration with the World Health Organisation (WHO) and published in a British medical journal, the Lancet, found that most abortions occur in developing countries—35m a year, compared with just 7m in rich countries.

【结构分析】

蓝色部分为句子的主干：The study （主语）found （谓语动词）that most abortions occur in developing countries—35m a year,compared with just 7m in rich countries （宾语从句）

2. 其余部分：carried out by the Guttmacher Institute in New York in collaboration with the World Health Organisation (WHO) and published in a British medical journal, the Lancet，是过去分词短语，作 study 的“非限制性定语”，前后有两个逗号。carried out 和 published 并列。相当于一个“非限制性定语从句”：which was carried out by the Guttmacher Institute in New York in collaboration with the World Health Organisation (WHO) and published in a British medical journal, the Lancet。

3. 在宾语从句中，compared with just 7m in rich countries 为过去分词短语，作从句的“比较状语”。

4. the Lancet 为 journal 的同位语；破折号后面的 35m a year，是对前句 abortions 的具体数字说明。

【翻译】这项研究由纽约古特马赫研究所与世界卫生组织合作进行并发表在英国医学杂志《柳叶刀》上，（研究）发现，大多数堕胎发生在发展中国家——每年3500万例，而富裕国家只有700万例。